Fuel cell employing local power generation when starting at low temperature

ABSTRACT

A fuel cell which can self-heat in a short time, in which no reaction gas is necessary for combustion, thereby improving the starting performance at low temperatures. The fuel cell comprises a cell structure in which an anode and a cathode are provided on either side of a solid polymer electrolyte membrane. This cell structure has a power generation plane and at least a part of the generation plane is defined as a local generation area so as to locally generate power. The fuel cell may include a pair of separators between which the cell structure is placed, and a reaction gas passage may be formed between the cell structure and each separator. One of a system for supplying a reaction gas to only a part of the reaction gas passage, and a system for supplying a reaction gas to the entire reaction gas passage is switchably selected.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a technique for activating afuel cell in a low-temperature atmosphere.

[0003] 2. Description of the Related Art

[0004] A typical example fuel cell has a membrane electrode assembly inwhich an anode and a cathode are provided on either side of a solidpolymer electrolyte membrane. The membrane electrode assembly is placedbetween a pair of separators so as to support the membrane electrodeassembly. In such a fuel cell, a fuel gas (e.g., hydrogen) is suppliedto a power generation plane of the anode, while an oxidizing gas (e.g.,air including oxygen) is supplied to a power generation plane of thecathode, so as to produce a chemical reaction. The electrons generatedin the chemical reaction flow to an external circuit, providing DC(direct current) electrical energy. An oxidizing gas such as oxygen orair is supplied to the cathode, and the hydrogen gas, electrons, andoxygen gas react at the cathode, thereby generating water. Therefore,the fuel cell has less effect on the surrounding environment and thushas become the focus of attention as a driving source for vehicles.

[0005] Generally, the operating temperature of this kind of fuel cell isapproximately 70 to 80° C. However, at low temperatures, the powergenerating efficiency is degraded; thus, it is difficult to obtainsatisfactory starting performance at a low temperature. Accordingly,when such a fuel cell employed in a vehicle is activated in a low outertemperature (e.g., below the freezing point), the starting operationrequires considerable time.

[0006] In order to solve this problem, Published Japanese TranslationNo. 2000-512068, of PCT International Publication No. WO97/48142,discloses a system in which electric power is supplied to an externalload of a fuel cell so as to promote the reaction and increase thetemperature due to self heating, thereby improving the startingperformance.

[0007] On the other hand, U.S. Pat. No. 6,103,410 discloses a system inwhich a portion of hydrogen which functions as a reaction gas is mixedwith air so as to produce a reaction by using a catalyst at the cathodeand to generate heat of combustion, thereby improving the startingperformance.

[0008] However, in the former method of using the self heating, if thetemperature of the fuel cell to be started is below the freezing point,considerable time is necessary for self-heating the entire fuel cellwhich has a large heat capacity. In the latter method of burning a partof the hydrogen, extra hydrogen used in the starting operation isnecessary in addition to hydrogen consumed in power generation; thus, alarger tank for storing hydrogen is necessary and the space forarranging peripheral components is limited.

[0009] In addition, the heat obtained by the self heating of the fuelcell may be insufficient for warming up the fuel cell at the start ofthe operation, and water generated in the fuel cell during the warmingup may freeze in the fuel cell.

SUMMARY OF THE INVENTION

[0010] In consideration of the above circumstances, an object of thepresent invention is to provide a fuel cell which can self-heat in ashort time, in which no reaction gas is necessary for combustion,thereby improving the starting performance at low temperatures.

[0011] Therefore, the present invention provides a fuel cell comprising:

[0012] a membrane electrode assembly (e.g., a membrane electrodeassembly 5 in an embodiment explained below) in which an anode (e.g., ananode 2 in the embodiment explained below) and a cathode (e.g., acathode 3 in the embodiment explained below) are provided on either sideof a solid polymer electrolyte membrane (e.g., a solid polymerelectrolyte membrane 4 in the embodiment explained below); wherein:

[0013] the membrane electrode assembly has a generation plane foroutputting power and at least a part of the generation plane is definedas a local generation area (e.g., a local generation area K in theembodiment explained below) to which a reaction gas is supplied so as tolocally generate power.

[0014] According to this structure, when the operation of the fuel cellis started at low temperatures, local power generation can be performedin a local area in the generation plane of the membrane electrodeassembly, so that self heating can be concentratedly performed in thelocal area, thereby quickly increasing the temperature. A producedhigh-temperature portion expands over the entire generation plane,thereby increasing the fuel cell.

[0015] Therefore, in comparison with the case in which the entire powergeneration plane is heated and thus the heated is broadened, the timenecessary for the starting the fuel cell can be reduced, therebyimproving the starting performance of the fuel cell at low temperatures.If the fuel cell is heated by combusting a combustion gas, a large tankfor storing the combustion gas is necessary. However, in the presentinvention, such a large tank is unnecessary and sufficient space forplacing peripheral functional elements can be obtained.

[0016] Typically, one of an entire plane generation mode, in which theentire generation plane is used for generation, and a local planegeneration mode, in which the local generation area is used for locallygenerating power, is switchably selected based on a temperature of thegeneration plane. Therefore, optimum operation control can be performedaccording to the temperature of the generation plane of the membraneelectrode assembly, thereby always obtaining optimum output andperforming suitable energy management.

[0017] The present invention also provides a fuel cell comprising:

[0018] a membrane electrode assembly in which an anode and a cathode areprovided on either side of a solid polymer electrolyte membrane; and

[0019] a pair of separators (e.g., separators 6 and 7 in an embodimentexplained below) between which the membrane electrode assembly isplaced, wherein the membrane electrode assembly is supported by theseparators, wherein:

[0020] a reaction gas passage (e.g., a reaction gas passage C or A inthe embodiment explained below) is formed between the membrane electrodeassembly and each separator, wherein a starting-mode reaction gaspassage system for supplying a reaction gas to a part of the reactiongas passage so as to locally generate power, and a normal-mode reactiongas passage system for supplying a reaction gas to the entire reactiongas passage so as to normally generate power are defined, and one of thestarting-mode reaction gas passage system and the normal-mode reactiongas passage system is switchably selected.

[0021] According to this structure, if the starting-mode reaction gaspassage system is used when the operation of the fuel cell is started atlow temperatures, the reaction gas is concentratedly supplied to a partof the reaction gas passage which substantially has a shorter passagelength, where the amount of the reaction gas supplied to the shorterpassage is the same as that of the reaction gas supplied in thenormal-mode reaction gas passage system.

[0022] Therefore, in comparison with the case in which the powergeneration using the entire generation plane is performed by supplyingthe reaction gas to the normal-mode reaction gas passage system and thusthe heated is broadened, the time necessary for the starting the fuelcell can be reduced, thereby improving the starting performance.

[0023] In the case of using the starting-mode reaction gas passagesystem, the flow velocity in the reaction gas passage is increasedbecause the shortened passage has lass resistance. According to theincrease of the flow velocity, the draining efficiency of watergenerated in the fuel cell is improved, and the residence time of thecooling liquid is reduced, thereby avoiding refreezing of the generatedwater.

[0024] Accordingly, also in this structure, local power generation canbe performed in a local area of the generation plane of the membraneelectrode assembly; thus, self heating can be concentratedly performedin the local area, thereby quickly heating this area. Such ahigh-temperature portion expands over the entire generation plane,thereby increasing the temperature of the fuel cell.

[0025] Typically, one of the starting-mode reaction gas passage systemand the normal-mode reaction gas passage system is switchably selectedbased on a temperature of the generation plane. For example, thestarting-mode reaction gas passage system may be used while thetemperature of the generation plane is a predetermined temperature(e.g., 0° C.) or below, and the system may be switched to thenormal-mode reaction gas passage system when the temperature exceeds thepredetermined temperature. Therefore, it is possible to always obtainoptimum output and perform suitable energy management.

[0026] The present invention also provides a fuel cell comprising:

[0027] a cell (e.g., a call 500 in an embodiment explained below) inwhich an anode and a cathode are provided on either side of a solidpolymer electrolyte membrane, and a reaction gas passage is formed ateach outer side of the pair of the anode and the cathode, wherein:

[0028] the cell has a generation plane for outputting power, and aheating device (e.g., an electric heater 33 or 53, a catalyst 65, or anoxidizing and reducing agent 72 in the embodiment explained below) forlocally heating the generation plane is provided at a part of thegeneration plane.

[0029] According to this structure, when the fuel cell is started at lowtemperatures, a part of the generation plane can be quickly heated.Therefore, the resistance of the ions which pass through this portion ofthe solid polymer electrolyte membrane can be reduced and the efficiencyof power generation can be improved. Accordingly, self heating can beimproved in the portion and the temperature of the portion can bequickly increased. This high-temperature portion then expands over theentire generation plane.

[0030] Typically, the heating device is an electric heater. In thiscase, the heating device can be driven by electrical energy.

[0031] The fuel cell may comprise a plurality of the cells which arestacked; and a stud bolt (e.g., a stud bolt 40A in the embodimentexplained below) for fastening the stacked cells, wherein the electricheater (e.g., an electric heater 53 in an embodiment explained below)may be built in the stud bolt. In this structure, the vicinity of thestud bolt can be locally heated.

[0032] The heating device may be a catalytic combustor (e.g., a catalyst65 in an embodiment explained below). In this case, when an oxidizinggas (e.g., oxygen or air) and a reducing gas (e.g., hydrogen) aresupplied to the catalytic combustor, these gases quickly bum and thus aportion of the generation plane can be quickly heated. Therefore, theheating device can have a simple structure, and such quick heating canfurther improve the starting performance of the fuel cell at lowtemperatures.

[0033] The heating device may include an oxidizing and reducing agent(e.g., an oxidizing and reducing agent 72 in an embodiment explainedbelow) which generates heat when being oxidized. Accordingly, a part ofthe generation plane can be quickly heated only by supplying anoxidizing gas (oxygen or air). Therefore, also in this case, the heatingdevice can have a simple structure, and the starting performance of thefuel cell at low temperatures can be further improved.

[0034] The present invention also provides a fuel cell system comprisinga fuel cell as explained above, and a controller for controlling theheating device according to a temperature in the fuel cell. Accordingly,the heating device can be driven only when the temperature of the fuelcell is low, so as to locally heat the generation plane of the cell, andwhile the temperature of the fuel cell is high, the heating device isnot driven so that the local heating of the cell can be stopped, therebyreducing energy consumption.

[0035] The present invention also provides a fuel cell system comprisinga fuel cell as explained above, and a controller for controlling theheating device according to an output voltage of the fuel cell.Accordingly, the heating device can be driven only when the outputvoltage of the fuel cell is low, so as to locally heat the generationplane of the cell, and while the output voltage of the fuel cell ishigh, the heating device is not driven so that the local heating of thecell can be stopped, thereby reducing energy consumption.

[0036] The present invention also provides a fuel cell system comprisinga fuel cell as explained above, which includes a plurality of the cellswhich are stacked; and a controller for controlling the heating deviceaccording to a temperature of each cell. In this structure, the heatingdevice can be driven or stopped in accordance with the temperature ofeach cell, thereby reducing energy consumption.

[0037] The present invention also provides a fuel cell system comprisinga fuel cell as explained above, which includes a plurality of the cellswhich are stacked; and a controller for controlling the heating deviceaccording to an output voltage of each cell. In this structure, theheating device can be driven or stopped in accordance with the outputvoltage of each cell, thereby reducing energy consumption.

[0038] The present invention also provides a fuel cell system comprisinga fuel cell as explained above, which includes a plurality of the cellswhich are stacked, and in at least one pair of the adjacent cells, theheating device is provided at a different position in the generationplane. According to this structure, when current flows between thesecells, the current flows in a direction perpendicular to the stackingdirection of the cells. Therefore, Joule heat is generated due to theelectric resistance of the current passage, so that the fuel cell isfurther heated. Accordingly, quicker heating can be performed and thestarting performance of the fuel cell at low temperatures can be furtherimproved.

[0039] The present invention also provides a fuel cell system comprisinga fuel cell as explained above; and a controller for controlling theheating device to generate a quantity of heat by which refreezing ofgenerated water in the fuel cell is avoided. Accordingly, heating usingthe heating device can be effectively performed, and the blockage of thereaction gas passage due to the freezing of water generated in the fuelcell can be gradually released, thereby reducing the time necessary forstarting the fuel cell.

[0040] The present invention also provides a fuel cell comprising:

[0041] a cell in which an anode and a cathode are provided on eitherside of a solid polymer electrolyte membrane, and a reaction gas passageis formed at each outer side of the pair of the anode and the cathode,and a first cooling liquid passage (e.g., a cooling liquid passage R inan embodiment explained below), separated from the reaction gas passage,is formed at a further outer side, wherein:

[0042] the cell has a generation plane for outputting power;

[0043] a second cooling liquid passage (e.g., a second cooling liquidpassage 36 in the embodiment explained below), independent of the firstcooling liquid passage, is formed on a part of the generation plane; and

[0044] cooling liquid, heated by an external heating device (e.g., anelectric heater 755 or 865 in the embodiment explained below) which isprovided outside the cell, is suppliable to the second cooling liquidpassage.

[0045] According to this structure, when the operation of the fuel cellis started at low temperatures, heated cooling liquid can be supplied tothe second cooling liquid passage, thereby quickly heating a part of thegeneration plane. Therefore, the resistance of the ions which passthrough this portion of the solid polymer electrolyte membrane can bereduced and the efficiency of power generation can be improved.Accordingly, self heating can be improved in the portion and thetemperature of the portion can be quickly increased. Thishigh-temperature portion then expands over the entire generation plane.Therefore, the time necessary for starting the fuel cell can be reduced.

[0046] The present invention also provides a fuel cell system comprisinga fuel cell as claimed above; and a controller for determining whetherthe heated cooling liquid is supplied to the second cooling liquidpassage.

[0047] This fuel cell system may further comprise:

[0048] a first cooling liquid circuit (e.g., a first cooling liquidcircuit 751 in the embodiment explained below) to which the firstcooling liquid passage is connected;

[0049] a second cooling liquid circuit (e.g., cooling liquid passages753 and 754 in the embodiment explained below) which has said heatingdevice (e.g., the electric heater 755) for heating the cooling liquid,wherein the second cooling liquid passage is connected via the secondcooling liquid circuit to the first cooling liquid circuit in parallelto the first cooling liquid passage; and

[0050] a passage switching section (e.g., control valves V1 and V2 inthe embodiment explained below) for permitting or prohibitingcommunication of the cooling liquid through the first cooling liquidpassage.

[0051] According to this structure, when the communication of thecooling liquid through the first cooling liquid passage is prohibited bythe passage switching section, the cooling liquid of the first coolingliquid circuit can be made to flow only through the second coolingliquid passage via the second cooling liquid circuit. In addition, thiscooling liquid supplied to the second cooling liquid passage can beheated by the heating device provided at the second cooling liquidcircuit. On the other hand, when the communication of the cooling liquidthrough the first cooling liquid passage is permitted by the passageswitching section, the cooling liquid through the first cooling liquidcircuit can be made to flow through the first cooling liquid passage.Therefore, a common device such as a pump can be used for supplyingheated cooling liquid to the first or second cooling liquid passage,thereby reducing the number of necessary parts and suppressing the cost.

[0052] Typically, the passage switching section is controlled accordingto a temperature in the fuel cell. Accordingly, when the temperature ofthe fuel cell is lower than a predetermined temperature, thecommunication of the cooling liquid through the first cooling liquidpassage can be prohibited by the passage switching section, and when thetemperature of the fuel cell is equal to or above the predeterminedtemperature, the communication of the cooling liquid through the firstcooling liquid passage can be permitted by the passage switchingsection. Therefore, it is possible to easily perform switching betweenthe entire plane generation and the local plane generation.

[0053] Instead of providing the second cooling liquid circuit and thepassage switching section, the fuel cell system may comprise:

[0054] a first cooling liquid circuit (e.g., a first cooling liquidcircuit 861 in an embodiment explained below) to which the first coolingliquid passage is connected;

[0055] a third cooling liquid circuit (e.g., a third cooling liquidcircuit 862 in the embodiment explained below) to which the secondcooling liquid passage is connected, wherein the third cooling liquidcircuit has said heating device (e.g., an electric heater 865 in theembodiment explained below) for heating the cooling liquid and isindependent of the first cooling liquid circuit. Accordingly, the amountof the cooling liquid maintained in the third cooling liquid circuit canbe small; thus, the cooling liquid can be rapidly heated, therebyquickly heating the fuel cell.

[0056] The present invention also provides a fuel cell system comprisinga fuel cell as explained above; and a controller for controlling theheating device to generate a quantity of heat by which refreezing ofgenerated water in the fuel cell is avoided. Accordingly, heating usingthe heating device can be effectively performed, and the blockage of thereaction gas passage due to the freezing of water generated in the fuelcell can be gradually released, thereby reducing the time necessary forstarting the fuel cell.

[0057] The present invention also provides a fuel cell comprising:

[0058] a membrane electrode assembly in which an anode and a cathode areprovided on either side of a solid polymer electrolyte membrane,wherein:

[0059] the membrane electrode assembly has a generation plane foroutputting power and at least a part of the generation plane is definedas a local generation area to which a reaction gas is supplied so as tolocally generate power; and

[0060] the local generation area is defined as a starting-mode poweroutput area (e.g., a starting-mode power output area D in an embodimentexplained below), and power is output from only the starting-mode poweroutput area in the local plane generation mode. Accordingly, power isconcentratedly output from the starting-mode power output area which isdefined in a local area of the generation plane. Therefore, this poweroutput area is concentratedly self-heated and the temperature of theportion is quickly increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061]FIG. 1 is a plan view showing the structure of the basicembodiment according to the present invention.

[0062]FIG. 2 is a sectional view along line A-A in FIG. 1.

[0063]FIG. 3 is a diagram for explaining the expansion of thehigh-temperature portion.

[0064]FIG. 4 is also a diagram for explaining the expansion of thehigh-temperature portion.

[0065]FIG. 5 is also a diagram for explaining the expansion of thehigh-temperature portion.

[0066]FIG. 6 is a plan view showing the structure of the firstembodiment (based on the basic embodiment) according to the presentinvention.

[0067]FIG. 7 is a plan view showing the structure of the secondembodiment according to the present invention.

[0068]FIG. 8 is a sectional view along line B-B in FIG. 7.

[0069]FIG. 9 is a plan view showing the structure of the thirdembodiment according to the present invention.

[0070]FIG. 10 is a plan view showing the structure of an example in thefourth embodiment according to the present invention.

[0071]FIG. 11 is a plan view showing the structure of another example inthe fourth embodiment.

[0072]FIG. 12 is a plan view showing the structure of another example inthe fourth embodiment.

[0073]FIG. 13 is a block diagram showing a fuel cell system forvehicles, as the fifth embodiment according to the present invention.

[0074]FIG. 14 is a plan view showing the distinctive portion of thefifth embodiment.

[0075]FIG. 15 is a sectional view along line X-X in FIG. 14.

[0076]FIG. 16 is a diagram showing the general structure of the fuelcell system in the fifth embodiment.

[0077]FIG. 17 is a flowchart showing the operation of the fifthembodiment.

[0078]FIG. 18 is a diagram showing the general structure of the fuelcell system as the sixth embodiment according to the present invention.

[0079]FIG. 19 is a diagram showing the general structure of the fuelcell as the seventh embodiment according to the present invention.

[0080]FIG. 20 is a longitudinal sectional view of the fuel cell as theeighth embodiment according to the present invention.

[0081]FIG. 21 is a flowchart showing an example of the control operationfor starting the fuel cell in the eighth embodiment.

[0082]FIG. 22 is a plan view showing a separator of the fuel cell as avariation of the eighth embodiment.

[0083]FIG. 23 is a plan view showing a separator of the fuel cell in theninth embodiment according to the present invention.

[0084]FIG. 24 is a cross-sectional view of the stud bolt in the fuelcell of the ninth embodiment.

[0085]FIG. 25 is a longitudinal sectional view of the fuel cell as thetenth embodiment according to the present invention.

[0086]FIG. 26 is a plan view showing a separator of the fuel cell in thetenth embodiment.

[0087]FIG. 27 is a flowchart showing an example of the control operationfor starting the fuel cell in the tenth embodiment.

[0088]FIG. 28 is a longitudinal sectional view of the fuel cell as theeleventh embodiment according to the present invention.

[0089]FIG. 29 is a plan view showing a separator of the fuel cell in theeleventh embodiment.

[0090]FIG. 30 is a plan view showing a positional relationship of thelocal generation area K between the adjacent cells in the twelfthembodiment according to the present invention.

[0091]FIG. 31 is a sectional view showing the direction of current whichflows between the adjacent cells in the twelfth embodiment.

[0092]FIG. 32 is a plan view showing a separator at the anode of thefuel cell in the thirteenth embodiment according to the presentinvention.

[0093]FIG. 33 is a longitudinal sectional view of the fuel cell in thethirteenth embodiment.

[0094]FIG. 34 is a rear view showing the separator at the anode in thethirteenth embodiment.

[0095]FIG. 35 is a flowchart showing an example of the control operationfor starting the fuel cell in the thirteenth embodiment.

[0096]FIG. 36 is a rear view showing a separator at the anode in avariation of the thirteenth embodiment.

[0097]FIG. 37 is a plan view showing a separator at the anode of thefuel cell in the fourteenth embodiment according to the presentinvention.

[0098]FIG. 38 is a flowchart showing an example of the control operationfor starting the fuel cell in the fourteenth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0099] Hereinafter, embodiments according to the present invention willbe explained with reference to the drawings.

[0100] First, an embodiment showing a basic structure of the presentinvention will be explained with reference to FIGS. 1 and 2.

[0101] As shown in FIG. 2, a fuel cell 1 has a membrane electrodeassembly 5 in which an anode 2 and a cathode 3 are provided on eitherside of a solid polymer electrolyte membrane 4. Each membrane electrodeassembly 5 is placed between a separator 6 at the anode 2 and aseparator 7 at the cathode 3 so as to support the membrane electrodeassembly 5. Plural membrane electrode assemblys 5 are stacked to obtain,for example, a fuel cell stack for vehicles. The stacked structure isfastened using stud bolts or the like. In this embodiment, a unit fuelcell having a pair of separators 6 and 7 between which the membraneelectrode assembly 5 is placed will be explained for convenience.

[0102] The solid polymer electrolyte membrane 4 is made of, for example,a perfluorosulfonic acid polymer. The main constituent of anode 2 andcathode 3 is platinum (Pt), which is placed on a diffusion layer made ofa porous carbon cloth or paper. The separators 6 and 7 are made ofcompacted carbon or metal. Electric power is output via the separators 6and 7.

[0103]FIG. 1 is a plan view showing the separator 7 observed from theside which faces the membrane electrode assembly 5. This separator 7 atthe cathode comprises an upper reaction gas passage C1 and a lowerreaction gas passage C2, that is, the reaction gas passage is dividedinto an upper half (i.e., C1) and a lower half (i.e., C2). If theseparator is made of compacted carbon, a plurality of grooves functionas the reaction gas passage, whereas if the separator is made of metal,a plurality of grooves formed by press molding or a passage formedbetween sealing materials functions as the reaction gas passage. Inaddition, the forms of the reaction gas passages C1 and C2 are notlimited, that is, the reaction gas passages C1 and C2 may be formed in azigzag, or they may be U-shaped. For convenience of explanation, thereaction gas passages of the separator 6 at the anode are also shown inFIG. 1 by chain lines.

[0104] The upper reaction gas passage C1 of the separator 7 at thecathode starts from an oxidizing gas inlet communication hole 10, whichis provided at the right side of the separator 7 and at a lower positionin the area assigned to C1, and ends at an oxidizing gas outletcommunication hole 11, which is provided at the left side of theseparator 7 and in a diagonal direction with respect to the inletcommunication hole 10.

[0105] The lower half of the separator 7 at the cathode also has thereaction gas passage C2 having a structure similar to that of C1, theinlet oxidizing gas communication hole 10, and the oxidizing gas outletcommunication hole 11.

[0106] The oxidizing gas inlet communication hole 10 is connected to asupercharger S/C via a supply passage 13; thus, air as an oxidizing gasis supplied to the oxidizing gas inlet communication hole 10 from thesupercharger S/C which is driven by a motor “m”. Here, a valve 14 forshutting off the air supply is attached to the supply passage 13connected to the lower reaction gas passage C2.

[0107] On the other hand, the separator 6 at the anode comprises anupper reaction gas passage A1 and a lower reaction gas passage A2, thatis, the reaction gas passage is divided into the upper half (i.e., A1)and the lower half (i.e., A2) which respectively correspond theabove-explained reaction gas passages C1 and C2. More specifically, theupper reaction gas passage A1 of the separator 6 at the anode startsfrom a fuel gas inlet communication hole 20, which is provided at theleft side of the separator 6 and at a lower position in the areaassigned to A1, and ends at a fuel gas outlet communication hole 21,which is provided at the right side of the separator 6 and in a diagonaldirection with respect to the inlet communication hole 20. The lowerhalf of the separator 6 also has the reaction gas passage A2 having astructure similar to that of A1, the fuel gas inlet communication hole20, and the fuel gas outlet communication hole 21. Accordingly, thereaction gas passage C1 and A1 have a crossing positional relationship,and the reaction gas passage C2 and A2 also have a crossing positionalrelationship.

[0108] The fuel gas inlet communication hole 20 is connected to ahydrogen tank H2 via a supply passage 23, and a valve 24 for shuttingoff the hydrogen gas supply is attached to the supply passage 23connected to the lower reaction gas passage A2. Instead of the hydrogentank, a methanol tank having a methanol gas reformer may be used.

[0109] A pair of cooling liquid inlet communication holes 30 and 30 areformed in the vicinity of the lower sides of the separator 6 (at theanode) and the separator 7 (at the cathode). Similarly, a pair ofcooling liquid outlet communication holes 31 and 31 are formed in thevicinity of the upper sides of the separators 6 and 7. In addition, acooling liquid passage R for connecting the inlet and outletcommunication holes 30 and 31 (which face each other) and cooling thefuel cell, is formed in the separator 7 at the anode. The cooling liquidpassages R are connected to piping for the cooling liquid (not shown).The cooling liquid may be pure water, ethylene glycol, oil or the like.

[0110]FIG. 2 is a sectional view along line A-A in FIG. 1. As shown inFIG. 2, a closed circuit 40 for outputting power of the fuel cell 1 isformed via terminals (not shown) connected to the above-explainedseparator 7 (at the cathode) and separator 6 (at the anode). The motor Mused for driving the vehicle and an external load F (which includes anelectric heater explained below) are driven by the power output from thefuel cell 1.

[0111] In FIG. 1, reference numeral 50 indicates an ECU (electriccontrol unit) connected to the hydrogen tank H2, the motor m providedfor the supercharger S/C, the valve 24 attached to the supply passage 23which is connected to the hydrogen tank H2, the valve 14 attached to thesupply passage 13 which is connected to the supercharger S/C, and atemperature sensor T in the fuel cell 1.

[0112] In each power generation plane of the cathode 3 and the anode 2,the area corresponding to the upper half of the separator (7 or 6)functions as a local generation area K, and the upper reaction gaspassages C1 and A1 of the separators 7 and 6 of the cathode 3 and anode2 function as starting-mode reaction gas passages (i.e., used when theoperation of the fuel cell is started).

[0113] Below, the functions of this basic embodiment will be explained.

[0114] In a lower-temperature atmosphere in which the outside airtemperature is, for example, below the freezing point (e.g., −10° C.),water, which is generated in the fuel cell 1 and which cannot be removedat the system stop, tends to freeze in a portion of the grooves of thereaction gas passages C1, C2, A1, and A2.

[0115] Therefore, when the operation of the fuel cell 1 is started, ifit is determined by the ECU 50 that the temperature of the fuel cell 1is equal to or below a predetermined temperature (e.g., 0° C.) based onthe detected temperature by the temperature sensor T, then the valves 14and 24 are closed. Here, the above temperature of the fuel cell 1 isactually the temperature of the cooling liquid or the separator.According to the above control of closing the valves, the oxidizing gasand the fuel gas are supplied to only the upper reaction gas passages C1and A1 which belong to the upper half of the separators 6 and 7.

[0116] Under these conditions, various auxiliary machines are activatedby a dedicated battery (not shown) for the auxiliary machines, and thesupercharger S/C is activated by a capacitor (not shown; a battery maybe used instead), so that air is supplied from the supercharger S/C viathe supply passage 13 and hydrogen is supplied from the hydrogen tank H2via the supply passage 23. Accordingly, a predetermined amount of airand hydrogen (i.e., corresponding to the flow rate, not assigned to thelocal-plane generation, but assigned to the entire plane generation) isconcentratedly supplied to the upper reaction gas passages C1 and A1which function as the starting-mode reaction gas passages. Therefore,each reaction gas (i.e., air or hydrogen) flows through the communicablereaction gas passage (among all the reaction gas passages), therebylocally generating power. In this process, the electrical energy isextracted via the external load F which includes the supercharger S/C;thus, only the upper half of the power generation planes self-heats dueto the reaction. Accordingly, the blockage of the reaction gas passagesC1 and A1 due to the freezing of the generated water (which wasgenerated in the fuel cell 1) can be effectively released.

[0117] In the portion where the local generation is performed, moregenerated water is generated. Therefore, the self heating should beperformed while the freezing of the newly-generated water is avoided.Accordingly, the following relationship must be satisfied:

(quantity of heat for avoiding freezing of generated water+quantity ofdischarged heat)<quantity of reaction heat (i.e., quantity of selfheating)  formula (1)

[0118] When the quantity of reaction heat (i.e., self heating) forsatisfying the above relationship is generated, the temperature of thelocal generation area K can exceed a predetermined temperature (e.g., 0°C.) before the operation of the fuel cell 1 stops due to decrease of thevoltage which is caused by the freezing of the generated water.Therefore, even if the remaining area (other than the local generationarea) is equal to or below the predetermined temperature (e.g., 0° C.),the generation of the fuel cell 1 can be maintained.

[0119] The supply of each reaction gas is concentrated to the localgeneration area K (i.e., ½ the area of the entire generation plane);thus, the amount of the reaction gas supplied to the upper reaction gaspassages C1 and A1 is increased (i.e., twice the amount in theentire-plane generation) and the self heating is further concentratedlyperformed. For example, the temperature of a part of the generationplane (see the area surrounded by a dashed line in FIG. 3) is quicklyincreased, thereby producing a high-temperature portion. Once such ahigh-temperature portion is produced, the high-temperature portiongradually expands due to the heat conduction, so that the frozengenerated water is further released and the function of the reaction gaspassages C1 and A1 is gradually recovered. This high-temperature portionexpands over the upper half (see the area surrounded by a dashed line inFIG. 4), and then towards the lower half, so that finally the entirepower generation plane of the fuel cell 1 is in the high-temperatureportion (see the area surrounded by a dashed line in FIG. 5).

[0120] When the temperature of the fuel cell 1, detected by thetemperature sensor T, reaches a predetermined temperature (e.g., 5° C.),the ECU 50 determines that the local generation operation of the fuelcell 1 should be terminated, and the ECU 50 opens the valves 14 and 24.Accordingly, hydrogen and air are supplied from the supply passages 13and 23 to both the upper reaction gas passages C1 and A1 and the lowerreaction gas passages C2 and A2, thereby switching the operation modefrom the local plane generation to the entire plane generation. That is,the reaction gases are supplied to all the reaction gas passages C1, A1,C2, and A2 of the fuel cell 1, so that rated output power can beobtained from the fuel cell 1 which has been transferred from the localplane generation.

[0121] As explained above, the local plane generation (i.e., theoperation of the fuel cell 1 for performing local plane generation) andthe entire plane generation (i.e., the operation of the fuel cell 1 forperforming entire plane generation) can be switched by the control ofthe ECU 50 according to the temperature of the power generation plane ofthe membrane electrode assembly 5, thereby performing operation controlsuitable for the temperature of the power generation plane of themembrane electrode assembly 5. Therefore, optimum power can always beobtained, and preferable energy management can be realized.

[0122] According to the above basic embodiment, a predetermined amountof the reaction gases supplied from the supercharger S/C and thehydrogen tank H2 are concentratedly supplied to the upper reaction gaspassages C1 and A1, which function as starting-mode reaction gaspassages, so as to perform local power generation. Therefore, the selfheating is also concentratedly performed in the target area to which alarger amount of the reaction gas is supplied. The temperature of thetarget area quickly increases, and such high-temperature portion expandsover the entire power generation plane, thereby increasing thetemperature of the fuel cell 1. If the reaction gases are supplied toall the reaction gas passages since the starting of the fuel cell 1 andthe entire power generation plane is used, the heated portion isbroadened. In comparison with this operation, in the present embodiment,the self-heated portion can be concentrated so that the time necessaryfor staring the fuel cell can be reduced and the starting performancecan be improved.

[0123] Even with the local plane generation, electric power necessaryfor the supercharger S/C or the other auxiliary machines can beacquired; thus, no problem occurs in the energy management for thestarting of the fuel cell. In addition, a predetermined amount of thereaction gas flows through each of the starting-mode reaction gaspassages C1 and A1; thus, the flow velocity in the reaction gas passageincreases and the remaining generated water in the passage can bequickly drained. Furthermore, the concentrated power generation canminimize the quantity of the discharged heat, so that the quantity ofheat can be increased and the fuel cell can be warmed in a short time.

[0124] First Embodiment

[0125] The first embodiment based on the above basic embodiment will beexplained with reference to FIG. 6.

[0126]FIG. 6 is a plan view showing the separator 7 at the cathode,observed from the side which faces the membrane electrode assembly.Similar to the above embodiment, the separator 7 also has the upper andlower reaction gas passages C1 and C2, which respectively correspond tothe upper and lower reaction gas passages A1 and A2 formed in theseparator at the anode (not shown in FIG. 6). Here, the parts identicalto those in the above-explained FIG. 2 are given identical referencenumerals.

[0127] The upper half of each power generation plane where the upperreaction gas passages C1 and A1 are formed is defined as a partiallyheated area B indicated by a dashed line, which thus fimctions as alocal generation area K. An electric heater (i.e., heating device notshown) such as a thin film heater is provided in an area correspondingto the partially heated area B. Here, power is supplied from a powersource (i.e., battery 60) to the electric heater; however, power may besupplied from the output power of the fuel cell.

[0128] In addition, a warm air blower for blowing warm air may be usedinstead of the electric heater.

[0129] Each oxidizing gas inlet communication hole 10, having astructure similar to that in the basic embodiment, is connected via thesupply passage 13 to the supercharger S/C, so that air as the oxidizinggas is equally supplied to the reaction gas passages C1 and C2 from thesupercharger S/C which is driven by the motor “m”. On the other hand,each fuel gas inlet communication hole 20 is connected via the supplypassage 23 to the hydrogen tank H2, and the hydrogen gas from the tankH2 is supplied to the upper and lower reaction gas passages A1 and A2.

[0130] The hydrogen tank H2, the motor m of the supercharger S/C, thebattery 60, and the temperature sensor T for measuring the temperatureof the fuel cell 1 are connected to the ECU 50.

[0131] The function of the first embodiment will be explained below.

[0132] When the operation of the fuel cell 1 is started, if it isdetected that the temperature of the fuel cell 1 is equal to or below apredetermined temperature (e.g., 0° C.) base on the detected result ofthe temperature sensor T, the ECU 50 switches the electric heater on, sothat the upper half of the fuel cell 1 is heated. Under theseconditions, the auxiliary machines are activated using a battery forthese machines, and air is supplied from the supercharger S/C via thesupply passage 13 to the reaction gas passages C1 and C2, while hydrogenis supplied from the hydrogen tank H2 via the supply passage 23 to thereaction gas passages A1 and A2.

[0133] According to the concentrated heating of the upper portion byusing the electric heater, the target portion of the solid polymerelectrolyte membrane is heated, and simultaneously, the catalyst of theanode and the cathode is activated, thereby improving the powergeneration efficiency. Therefore, local generation is quickly performedin the partially heated area B. According to the quick generation, selfheating due to the reaction is promoted, so that the target area isquickly heated by the heating using the electric heater and the selfheating. This high-temperature portion then expands over the entirepower generation plane, so that the temperature of the entire fuel cell1 is increased.

[0134] In the portion where the local generation is performed, moregenerated water is generated after the generation starts. Therefore, theself heating should be performed while the heating using the electricheater is performed and freezing of the newly-generated water isavoided. Accordingly, the following relationship must be satisfied:

(quantity of heat for avoiding freezing of generated water+quantity ofdischarged heat)<(quantity of reaction heat (i.e., quantity of selfheating)+quantity of heating using the heater)  formula (2)

[0135] When the temperature detected by the temperature sensor T reachesa predetermined temperature (e.g., 5° C.), the ECU 50 determines thatthe local generation should be terminated and stops the electric heater,so that the local plane generation is switched to the entire planegeneration. Accordingly, the entire plane power generation without usingthe electric heater is performed, and rated power can be output from thefuel cell 1.

[0136] In addition to the effects obtained by the basic embodiment, inthe first embodiment, self heating of the fuel cell 1 can be assistedusing the electric heater and the temperature of the partially heatedarea B can be quickly increased. This high-temperature portion expandsover the entire power generation plane, thereby efficiently increasingthe temperature of the fuel cell 1. Therefore, in comparison with thecase in which the entire power generation plane is heated, aconcentrated self-heated portion is obtained and thus the time necessaryfor the starting the fuel cell can be reduced, thereby improving thestarting performance. In particular, the quantity of heating using theelectric heater can be controlled so as to prevent the freezing of thenewly-generated water, thereby performing effective heating. Therefore,the blockage of the reaction gas passages due to the freezing of thegenerated water can be gradually released and the time for starting thefuel cell can be reduced.

[0137] Second Embodiment

[0138] The second embodiment based on the basic embodiment will beexplained with reference to FIGS. 7 and 8.

[0139]FIG. 7 is a plan view showing the separator 7 at the cathode,observed from the side which faces to the membrane electrode assembly 5.

[0140] In this embodiment, each of the separator 7 at the cathode andthe separator 6 at the anode is divided into an upper half and a lowerhalf via an insulating material 70, and thus the upper half and thelower half are electrically insulated. Therefore, power can beindependently output from the upper half, that is, the upper halffunctions as a starting-mode power output area D.

[0141] As shown by FIG. 7, the separator 7 at the cathode in the presentembodiment also comprises upper and lower reaction gas passages C1 andC2 assigned to the upper and lower halves, where the reaction gaspassages C1 and C2 respectively correspond to reaction gas passages A1and A2 which are formed in the upper and lower halves of the separator 6at the anode. In FIG. 7, parts identical to those in the basicembodiment are given identical reference numerals.

[0142] The upper half of each power generation plane, where the upperreaction gas passages C1 and A1 are provided, is defined as thestarting-mode power output area D (i.e., local generation area K).

[0143]FIG. 8 is a sectional view along line B-B in FIG. 7. As shown inFIG. 8, closed circuits 41 and 42 for outputting power from the fuelcell 1 are formed by attaching terminals (not shown) to the upper andlower halves of the separators 7 and 6. The output power from the fuelcell 1 is supplied to the driving motor M and the battery for theauxiliary machines, and used for driving the external load F whichincludes the motor “m” for supercharger S/C. A switch 43 is inserted inthe closed circuit 42 at the lower half side.

[0144] Each oxidizing gas inlet communication hole 10, having astructure similar to that in the basic embodiment, is connected via thesupply passage 13 to the supercharger S/C, so that air as the oxidizinggas is equally supplied to the reaction gas passages C1 and C2 from thesupercharger S/C which is driven by the motor m. On the other hand, eachfuel gas inlet communication hole 20 is connected via the supply passage23 to the hydrogen tank H2, and the hydrogen gas from the tank H2 issupplied to the upper and lower reaction gas passages A1 and A2.

[0145] The hydrogen tank H2, the motor m of the supercharger S/C, thebattery 60, the temperature sensor T for measuring the temperature ofthe fuel cell 1, and the switch 43 in the lower half portion areconnected to the ECU 50.

[0146] A cooling liquid inlet communication hole 30 and a cooling liquidoutlet communication hole 31 which communicates with the inletcommunication hole 30 are formed in the vicinity of each lower side ofthe separators 6 and 7, and a U-shaped cooling liquid passage R isformed in the lower half of the separator 6 at the anode. Also in thevicinity of each upper end of the separators 6 and 7, a cooling liquidinlet communication hole 30 and a cooling liquid outlet communicationhole 31 which communicates with the inlet communication hole 30 areformed, and a U-shaped cooling liquid passage R is formed in the upperhalf of the separator 6 at the anode. That is, the separators 6 and 7are divided into upper and lower halves by the insulating material 70 asexplained above; thus, the communicable cooling liquid passages R arerespectively and independently formed in the upper and lower halves.Each cooling liquid passage R is connected to piping (not shown) for thecooling liquid.

[0147] The function of the second embodiment will be explained below.

[0148] When the fuel cell 1 is started, if it is detected that thetemperature of the fuel cell 1 is equal to or lower than a predeterminedtemperature (e.g., 0° C.), the switch 43 is switched off by the ECU 50,so that the closed circuit 42 at the lower halves of the separators 6and 7 is shut off and the power output is performed only via the closedcircuit 41 at the upper halves of the separators 6 and 7.

[0149] Under these conditions, the auxiliary machines are activated bythe dedicated battery, and air is supplied from the supercharger S/C viathe supply passage 13 to the reaction gas passages C1 and C2, whilehydrogen is supplied from the hydrogen tank H2 via the supply passage 23to the reaction gas passages A1 and A2.

[0150] As the closed circuit 42 is shut off, power is not output fromthe lower halves of the separators 6 and 7, that is, power generation isnot performed in the lower area. In contrast, in the upper halves of theseparators 6 and 7, power is output while the reaction gases aresupplied; thus, in the upper area, the resistance of the ions which passthrough the solid polymer electrolyte membrane 4 is large even in alow-temperature atmosphere, and self heating is concentratedlyperformed. That is, dispersion of the self heating, which is observed inthe entire plane power generation, can be avoided and the self heatingcan be concentratedly performed in the upper half of each separator.Accordingly, the blockage of the reaction gas passages due to the frozengenerated water can be efficiently released.

[0151] Similar to the above embodiments, in the portion where the localgeneration is performed, more generated water is generated. Therefore,the self heating should be performed while the freezing of thenewly-generated water is avoided. Accordingly, the followingrelationship must be satisfied:

(quantity of heat for avoiding freezing of generated water+quantity ofdischarged heat)<quantity of reaction heat (i.e., quantity of selfheating)  formula (3)

[0152] Therefore, the self heating is further concentratedly performed,and the temperature of the upper half is quickly increased, therebyproducing a high-temperature portion. Once such a high-temperatureportion is produced, the high-temperature portion gradually expands dueto the heat conduction, so that the freezing of the generated water isfurther released and the function of the reaction gas passages C1 and A1is gradually retrieved. This high-temperature portion expands over theupper half, and then towards the lower half, so that finally, the entirepower generation plane of the fuel cell 1 belongs to thehigh-temperature portion.

[0153] When the temperature of the fuel cell 1, detected by thetemperature sensor T, reaches a predetermined temperature (e.g., 5° C.),the termination of the local plane generation is determined by the ECU50 and the ECU 50 switches the switch 43 on so as to release theshut-off state of the closed circuit 42 at the lower halves of theseparators. Accordingly, power is also output from the lower halves ofthe separators 6 and 7, thereby switching from the local generationoperation to the entire generation operation, and rated power can beobtained from the entire fuel cell 1.

[0154] According to the second embodiment, in addition to theabove-explained embodiments, the self heating portion can be efficientlyconcentrated in comparison with the case in which power is output fromthe entire generation plane, so that the time necessary for starting thefuel cell 1 can be reduced, thereby improving the starting performance.

[0155] Third Embodiment

[0156] Another embodiment will be explained below. FIG. 9 is a plan viewshowing the separator 7 at the cathode, observed from the side whichfaces the membrane electrode assembly. In the above embodiments, thereaction gas passages are divided into upper and lower portions so as toform a local generation area. However, as shown in FIG. 9, the localgeneration area K may be defined without dividing the reaction gaspassages.

[0157] The separator 7 at the cathode is made of metal, and the reactiongas passage is formed by using seal members G. Reference numeral 30indicates a cooling liquid inlet communication hole, while referencenumeral 31 indicates a cooling liquid outlet communication hole. Here,explanations of the separator at the anode are omitted.

[0158] The separator 7 at the cathode has an oxidizing gas inletcommunication hole 10 formed in an upper portion on the right side, andan oxidizing gas outlet communication hole 11 formed in a lower portionon the right side, where a U-shaped reaction gas passage C is formed.The separator 7 also has a fuel gas inlet communication hole 20 formedin an upper portion on the left side, and a fuel gas outletcommunication hole 21 formed in a lower portion on the left side, wherea U-shaped reaction gas passage is formed in the separator at the anode(not shown).

[0159] In this embodiment, an electric heater is attached to the areasurrounded by a dashed line, that is, to a part of the upper half of thepower generation plane. This area is a partially heated area B, that is,a local generation area K.

[0160] In addition to the effects obtained by the above embodiments,according to the present embodiment in which the local generation area Kis close to the oxidizing gas inlet communication hole 10 and fuel gasinlet communication hole 20, each reaction gas is reliably consumed forthe power generation. Therefore, the high-temperature portion due to theself heating can be reliably formed. Additionally, the generated watertends to remain downstream of the reaction gas passage C; thus, in thelocal generation area K at the upstream side, generated water is noteasily frozen, so that the reaction gas can be reliably supplied.

[0161] Fourth Embodiment

[0162] In the fourth embodiment shown in FIGS. 10 to 12, the reactiongas passages are divided into the upper and lower halves. Similar to theprevious embodiment, the following examples have a separator made ofmetal, and the passage is formed by sealing materials G. Also in thefollowing examples, the cooling liquid inlet communication hole 30 andthe cooling liquid outlet communication hole 31 are respectivelyprovided at the left and right sides of the separator.

[0163] Also in the present embodiment, the upper (or lower) half can bedefined as a local generation area. That is, starting-mode reaction gaspassages C1 and A1, a partially heated area B, and a starting-mode poweroutput area D can be defined, so that similar to the above embodiments,the starting time of the fuel cell can be reduced and the startingperformance can be improved.

[0164] More specifically, in the example shown in FIG. 10, the oxidizinggas inlet communication hole 10 and the oxidizing gas outletcommunication hole 11 are provided in an upper portion at either side,while the fuel gas inlet communication hole 20 and the fuel gas outletcommunication hole 21 are provided in a lower portion at either side. Inthis example, the generated water does not easily remain in an upperportion of the upper reaction gas passage C1; thus, the local generationcan be effectively performed by using this upper portion.

[0165] In another example shown in FIG. 11, an oxidizing gas inletcommunication hole 10 and an oxidizing gas outlet communication hole 11are respectively provided in upper and lower portions on the right side,while a fuel gas inlet communication hole 20 and a fuel gas outletcommunication hole 21 are respectively provided in upper and lowerportions on the left side, where a U-shaped reaction gas passage C1 isformed (refer to the U-shaped reaction gas passage in FIG. 9).

[0166] In another example shown in FIG. 12, an oxidizing gas inletcommunication hole 10 and an oxidizing gas outlet communication hole 11are respectively provided in an upper portion on the right side and alower portion on the left side, while a fuel gas inlet communicationhole 20 and a fuel gas outlet communication hole 21 are respectivelyprovided in an upper portion on the left side and a lower portion on theright side, where reaction gas passages C1 and C2 are formed in azigzag.

[0167] In the embodiments explained above, the power generation plane isgenerally divided into upper and lower halves, so as to form a localgeneration area. However, the division form is not limited, for example,the power generation plane may be divided into right and left halves, orany small area may be defined as a local generation area. Since thegenerated water tends to remain in a lower portion, the local generationis preferably performed in an upper portion where less generated waterremains. In addition, the generated water tends to remain downstream ofeach reaction gas passage; thus, the local generation is preferablyperformed in the upstream of each reaction gas passage.

[0168] Fifth Embodiment

[0169]FIG. 13 is a block diagram showing a fuel cell system forvehicles, in the fifth embodiment based on the basic embodiment.

[0170] In all the following embodiments, parts identical to thoseexplained in the above embodiments are basically given identicalreference numerals.

[0171] The fuel cell 1 is connected in parallel to a capacitor 100,which functions as a battery device (so that a battery may be usedinstead), and a current limiter 200. To the current limiter 200, asupercharger S/C for supplying air, and other loads including a drivingmotor, are connected as load F.

[0172] The current limiter 200 is provided for protecting the fuel cell1 in an abnormal state in which the generation voltage or the state ofgas supply has a problem. The protection by the current limiter 200 isperformed by limiting the output power of the fuel cell 1. In the normalstate, the fuel cell 1 and each electric load are electrically anddirectly coupled with each other.

[0173] Reference numeral 300 indicates an ECU for driving the drivingmotor based on the degree of opening of an accelerator pedal 400, wherethe degree of opening reflects the intention of the driver of thevehicle. The ECU 300 also controls the rotation speed of thesupercharger S/C according to a required power value for the fuel cell1, which is determined by adding the power of the driving motor and thepower of the electric loads which include the supercharger S/C.

[0174] That is, according to a output request signal from the ECU 300, arequired amount of power is supplied from the fuel cell 1 to eachelectric load, within the range limited by the current limiter 200.Therefore, if a specific required power value is output from the ECU 300at the starting of the system, the supercharger S/C operates accordingto an idle output (i.e., output in the idle mode) so that a specificamount of air is supplied to the fuel cell 1 and a corresponding amountof hydrogen gas is also supplied to the fuel cell 1. During this processfor satisfying the required idle output, an amount of the reaction gasis supplied to a portion of the reaction gas passage (explained below),where this amount is equivalent to that supplied when the entirereaction gas passage is used. Therefore, the self heating isconcentratedly performed because the consumption of the reaction gas isthe same as that in the entire generation, and power equal to thatoutput in the entire generation is output.

[0175]FIGS. 14 and 15 show distinctive elements in the presentembodiment. As shown in FIG. 14, the separator 7 at the cathode has areaction gas passage C formed in a zigzag. This reaction gas passage Cstarts from an oxidizing gas inlet communication hole 10 provided in alower portion at the right side, and ends at an oxidizing gas outletcommunication hole 11 provided in an upper portion at the left side,that is, in a diagonal direction with respect to the inlet communicationhole 10.

[0176] The separator 6 at the anode also has a reaction gas passage A(shown by a chain line) which also has a zigzag form corresponding tothe reaction gas passage C. More specifically, the reaction gas passageA and the reaction gas passage C have a crossing positionalrelationship. Therefore, the reaction gas passage A starts from a fuelgas inlet communication hole 20 provided in a lower portion at the leftside, and ends at a fuel gas outlet communication hole 21 provided in anupper portion at the right side, that is, in a diagonal direction withrespect to the inlet communication hole 20. A pair of cooling liquidinlet communication holes 30 and 30 is formed at the lower sides of theseparators 6 and 7, while a pair of cooling liquid outlet communicationholes 31 and 31 is formed at the upper sides of the separators 6 and 7.A cooling liquid passage R for connecting the cooling liquid inlet andoutlet communication holes 30 and 31, which face each other, is formedin the separator 6 at the anode.

[0177] As shown in FIG. 15, which is a sectional view along line X-X inFIG. 14, a closed circuit 40 for outputting power from the fuel cell 1is formed via terminals attached to the separators 7 and 6.

[0178] An auxiliary gas supply inlet 114 is provided relatively close tothe oxidizing gas outlet communication hole 11 for the reaction gaspassage C, where the auxiliary gas supply inlet 114 is connected to abranch end 113 of a branch passage 112 (explained below). Also for thereaction gas passage A of the separator 6, an auxiliary gas supply inlet115 is formed at a symmetrical position with respect to the auxiliarygas supply inlet 114 (see FIG. 14). The auxiliary gas supply inlet 115is also connected to a branch end of a branch passage.

[0179] The portion between the auxiliary gas supply inlet 114 and theoxidizing gas outlet communication hole 11 functions as a localgeneration reaction gas passage C3, while the portion between theauxiliary gas supply inlet 115 and the fuel gas outlet communicationhole 21 functions as a local generation reaction gas passage A3. In thepower generation plane of the membrane electrode assembly 5, the areacorresponding to the local generation reaction gas passages C3 and A3functions as a local generation area K. The auxiliary gas supply inlets114 and 115 are positioned in order that the local generation reactiongas passages C3 and A3 partially overlap with each other.

[0180] As shown in FIG. 16 in which the fuel cell 1 is simplified, a gassupply passage 16 is connected to the oxidizing gas inlet communicationhole 10 and a gas discharge passage 17 is connected to the oxidizing gasoutlet communication hole 11 in the separator 7 at the cathode. Inaddition, a branch passage 112 is connected to the gas supply passage16, and the (branch) end 113 of the branch passage 112 is connected tothe auxiliary gas supply inlet 114 provided in the middle of thereaction gas passage C.

[0181] A valve VB is inserted in the gas supply passage 16, while avalve VA is inserted in the branch passage 112. According to the openingand closing control of the valves VA and VB, the air as the oxidizinggas can be supplied, not from the gas supply passage 16, but from thebranch passage 112 to the auxiliary gas supply inlet 114.

[0182] A gas supply system 80 including the supercharger S/C and thelike is attached to the gas supply passage 16 which is connected to theoxidizing gas inlet communication hole 10, and a discharged gasprocessing system 90 is attached to the gas discharge passage 17 whichis connected to the oxidizing gas outlet communication hole 11. The gassupply system 80, the discharged gas processing system 90, and thevalves VA and VB are connected to the ECU 300. A temperature sensor Tfor detecting the temperature in the fuel cell is also connected to theECU 300.

[0183] Accordingly, the starting-mode reaction gas passage system forgenerating power by supplying the reaction gas to the local generationreaction gas passage C3 and the normal-mode reaction gas passage systemfor generating power by supplying the reaction gas to the entirereaction gas passage are switchable by using the valves VA and VB.

[0184] In this embodiment, a communication passage 18 is providedbetween the gas supply passage 16 (here, the portion between the valveVB and the oxidizing gas inlet communication hole 10) and the gasdischarge passage 17. A valve VC, which is also connected to the ECU300, is inserted in the communication passage 18.

[0185] The anode side also has a gas supply system which includes ahydrogen tank and the like, a gas supply passage connected to the fuelgas inlet communication hole 20, and a gas discharge passage connectedto the fuel gas outlet communication hole 21, where the end of a branchpassage is connected to the auxiliary gas supply inlet 115. That is, theanode side has a structure similar to that of the cathode side; thus,explanations thereof are omitted.

[0186] The operation of the present embodiment will be explained withreference to the flowchart in FIG. 17.

[0187] In the first step S01 in FIG. 17, when an ignition switch isswitched on, a specific valve control routine is executed (see stepS02). Specifically, this control routine is a valve control operationnecessary for starting the fuel cell, such as purging of the generatedwater by using a purge valve (not shown).

[0188] In step S03, it is determined whether temperature “t” in the fuelcell 1, measured using the temperature sensor T, is above 0° C. If theresult of the determination is “YES”, the operation proceeds to stepS04, while if the result of the determination is “NO”, the operationproceeds to step S06, where the operation mode is shifted to alow-temperature starting mode, which will be explained below.

[0189] After step S06, step S08 is executed. In step S08, it isdetermined whether the temperature “t” measured by the temperaturesensor T is above 0° C. If the result of the determination is “YES”, theoperation proceeds to step S04, while if the result of the determinationis “NO”, the operation proceeds to step S06, where the low-temperaturestarting mode is maintained.

[0190] The threshold used in the above step S08 may be changeableaccording to the quantity of the load connected to the fuel cell. Forexample, when a high load is connected, the operation proceeds to stepS04 if the temperature in the fuel cell exceeds 0° C.; however, when alow load is connected, the operation does not proceed to step S204 untilthe temperature in the fuel cell exceeds 5° C. This is because the lowload has a relatively low heating value in comparison with the highload, and thus it is preferable to shift the normal power generationmode after the temperature reaches a higher level.

[0191] In step S04, it is determined whether an external trigger, whichis an operation button for shifting to a stop sequence mode, is off. Ifthe result of the determination is “YES”, that is, if the operationbutton has not been pushed, then the operation proceeds to step S05 soas to shift to the normal power generation mode. After step S05, thedetermination in step S04 is repeated. If the result of thedetermination is “NO”, that is, if the operation button has been pushed,then the operation proceeds to step S07 so as to shift to the stopsequence mode (explained below). The operation of this flow is thencompleted.

[0192] Each operation mode will be explained with reference to FIG. 16.

[0193] In the normal power generation mode in step S05, the valves VAand VC are closed, while the valve VB is opened. Therefore, the airsupplied from the gas supply system 80 is supplied from the gas supplypassage 16 and the oxidizing gas inlet communication hole 10 to theentire reaction gas passage C. This supplied air reacts with thehydrogen gas which is similarly supplied to the reaction gas passage Aat the anode (not shown), so that the entire plane generation of themembrane electrode assembly 5 is performed and electrical energy isgenerated. This electrical energy is supplied via the closed circuit 40(see FIG. 15) to the load F and the driving motor M. The gas which hasbeen used in the reaction is then discharged via the oxidizing gasoutlet communication hole 11 from the gas discharge passage 17 to thedischarged gas processing system 90.

[0194] In the low-temperature starting mode in step S06, the valve VA isopened, while the valves VB and VC are closed. Therefore, the airsupplied from the gas supply system 80 is supplied via the branchpassage 112 and the auxiliary gas supply inlet 114 to the localgeneration reaction gas passage C3. This supplied air reacts with thehydrogen gas which is similarly supplied to the local generationreaction gas passage A3 at the anode (not shown), so that the localplane generation using a part of the generation plane of the membraneelectrode assembly 5 is performed and electrical energy is generated.This electrical energy is supplied via the closed circuit 40 (see FIG.15) to the loads F which includes the motor for driving the superchargerS/C, which is necessary in the idle mode. The gas which has been used inthe reaction is then discharged via the oxidizing gas outletcommunication hole 11 from the gas discharge passage 17 to thedischarged gas processing system 90.

[0195] In the above process, the reaction gas, whose amount is equal tothat supplied in the entire generation, is concentratedly supplied tothe local generation reaction gas passage C3 (or A3) which has a shorterpassage. Therefore, self heating is concentratedly performed. Inaddition, the flow velocity in the reaction gas passage is increasedbecause the shortened passage has lass resistance. Therefore, thetemperature in the relevant area quickly increases, and thehigh-temperature portion then expands over the entire generation plane,thereby increasing the temperature of the fuel cell 1.

[0196] When the increasing temperature of the fuel cell 1 exceeds apredetermined temperature (e.g., 0° C.), that is, if the result of thedetermination in steps S03 and S08 is “YES”, the operation mode isshifted to the normal power generation mode. When this mode shift isperformed, the valve VC may be slightly opened so as to increase theamount of the reaction gas which passes through the passage connected tothe auxiliary gas supply inlet 114, so that the defrosted generatedwater in this passage can be drained.

[0197] In the stop sequence mode in step S07, in order to improve therestarting performance of the (stopped) fuel cell 1, the generated waterremains in the reaction gas passage C is drained before stopping thefuel cell 1. In this mode, the valve VA is opened, the valve VB isclosed or slightly opened, and the valve VC is closed. Accordingly, theflow velocity in the local generation reaction gas passage C3 isincreased, so that the draining efficiency of the generated water isimproved. Therefore, it is possible to reliably prevent the generatedwater in the reaction gas passage C3 from freezing. In addition, theflow velocity of the reaction gas in the reaction gas passage C3 can becontrolled by controlling the degree of opening of the valve VB.Furthermore, the generated water generated at the lower side of thepower generation plane of the membrane electrode assembly 5 can bedrained by slightly opening the valve VB.

[0198] According to the present embodiment, in the operation using thestarting-mode reaction gas passage, the reaction gas is supplied to ashorter reaction gas passage (i.e., C3 and A3). Therefore, the sameelectric power as that output in the entire plane generation is outputfrom a portion of the power generation plane, so that self heating isconcentratedly performed. Therefore, the flow velocity in the shorterreaction gas passage is increased, thereby improving the drainingcapability of the generated water. In addition, the reaction gas staysin the shorter reaction gas passage for a shorter time, thereby avoidingrefreezing of the generated water.

[0199] If the fuel cell is heated by combusting a combustion gas, alarge tank for storing the combustion gas is necessary. However, in thepresent embodiment, such a large tank is unnecessary and sufficientspace for placing peripheral functional elements can be obtained.

[0200] In addition, according to the temperature of the fuel cell 1, thestarting-mode reaction gas passage system and the normal-mode reactiongas passage system can be switchably used in the operation of the fuelcell. Typically, based on a threshold temperature (e.g., 0° C.), thestarting-mode reaction gas passage system is used when the temperatureof the fuel cell is equal to or below the threshold temperature, whilethe normal-mode reaction gas passage system is used when the temperatureof the fuel cell is above the threshold temperature, thereby alwaysobtaining optimum output according to the temperature of the fuel celland performing suitable energy management.

[0201] In the present embodiment, the local generation can be performedusing a simple structure in which the branch passage 112 is used and thebranch end 113 of this branch passage 112 is connected to the auxiliarygas supply inlet 114; thus, the fuel cell system can be easilymanufactured.

[0202] Sixth Embodiment

[0203]FIG. 18 shows the sixth embodiment, in which the separator 7 atthe cathode has a reaction gas passage C consisting of plural reactiongas passages CC (e.g., two reaction gas passages) which are adjacentwith each other. Similar to the previous embodiment, a gas supplypassage 16 is connected to the oxidizing gas inlet communication hole10, a branch passage 112 having a valve VA is connected to the gassupply passage 16, and the gas supply system 20 is connected to the gassupply passage 16.

[0204] In this embodiment, two oxidizing gas outlet communication holes212 and 213 are formed in correspondence to two reaction gas passagesCC, and two gas discharge passages 17 and 17 are connected to theseoxidizing gas outlet communication holes 212 and 213. Each gas dischargepassage 17 is connected via a junction passage 19 to the discharged gasprocessing system 90. In the junction passage 19, a valve VC is insertedat the position where two flows from the gas discharge passages meet.The branch end 113 of the branch passage 112 is connected to the gasdischarge passage 17 between the valve VC and the upper oxidizing gasinlet communication hole 212.

[0205] A bypass portion 123 for making the adjacent reaction gaspassages CC communicate with each other is formed in the vicinity of theoxidizing gas outlet communication holes 212 and 213. Therefore, aU-shaped local generation reaction gas passage CC1 is formed between theoxidizing gas outlet communication holes 212 and 213 and the bypassportion 123. Accordingly, the starting-mode reaction gas passage systemfor performing the local generation by supplying the reaction gas to thereaction gas passage CC1, and the normal-mode reaction gas passagesystem for generating power by supplying the reaction gas to the entirereaction gas passage C can be switchably used using valves VA, VB, andVC. Therefore, a portion of the membrane electrode assembly 5, whichcorresponds to the local generation reaction gas passage CC1, is definedas a local generation area K (see the circle indicated by “K” in FIG.18).

[0206] The anode side has a similar structure, and explanations thereofare also omitted in this embodiment.

[0207] The function of the present embodiment will be explained below.

[0208] In this embodiment, one of the normal power generation mode, thelow-temperature starting mode, and the stop sequence mode is selectedaccording to a process similar to that shown in FIG. 17; thus, aflowchart showing the operation of the present embodiment is omitted.

[0209] The operation of each mode will be explained with reference toFIG. 18 (FIG. 15 is also referred to).

[0210] In the normal power generation mode, the valve VA is closed,while the valves VB and VC are opened. Therefore, the air supplied fromthe gas supply system 80 is supplied from the gas supply passage 16 andthe oxidizing gas inlet communication hole 10 to the entire reaction gaspassage C. This supplied air reacts with the hydrogen gas which issimilarly supplied to the reaction gas passage at the anode (not shown),so that the entire plane generation using the entire plane of themembrane electrode assembly 5 is performed and electrical energy isgenerated. This electrical energy is supplied via the closed circuit 40(see FIG. 15) to the load F and the driving motor M. The gas which hasbeen used in the reaction is then discharged via the oxidizing gasoutlet communication holes 212 and 213 from the two gas dischargepassages 17 and 17 to the discharged gas processing system 90.

[0211] In the low-temperature starting mode, the valve VA is opened,while the valves VB and VC are closed. Therefore, the air supplied fromthe gas supply system 80 is supplied via the branch passage 112, theupper gas discharge passage 17, and the upper oxidizing gas outletcommunication hole 212 to the U-shaped local generation reaction gaspassage CC1. This supplied air reacts with the hydrogen gas which issimilarly supplied to the local generation reaction gas passage at theanode (not shown), so that the local plane generation using a part ofthe generation plane of the membrane electrode assembly 5 is performedand electrical energy is generated. This electrical energy is suppliedvia the closed circuit 40 (see FIG. 15) to the loads F which include themotor for driving the supercharger S/C, which is necessary in the idlemode. The gas which has been used in the reaction is then discharged viathe lower oxidizing gas outlet communication hole 213 from the lower gasdischarge passage 17 to the discharged gas processing system 90.

[0212] In the above process, the reaction gas, whose amount is equal tothat supplied in the entire generation, is concentratedly supplied tothe local generation reaction gas passage CC1 which has a shorterpassage. Therefore, self heating is concentratedly performed. Inaddition, the flow velocity in the reaction gas passage CC1 is increasedbecause the shortened passage has less resistance. Therefore, thetemperature in the relevant area quickly increases, and thehigh-temperature portion then expands over the entire generation plane,thereby increasing the fuel cell 1. In particular, a U-shaped passage CChaving a smaller cross-sectional area is used as the local generationreaction gas passage CC1; thus, the flow velocity can be much morequickly increased.

[0213] When the increasing temperature of the fuel cell 1 exceeds apredetermined temperature (e.g., 0° C.), the operation mode is shiftedto the normal power generation mode. When this mode shift is performed,the valve VB may be slightly opened so as to supply the reaction gas tothe upstream of the reaction gas passage C (i.e., upstream relative tothe bypass portion 123), so that the defrosted generated water in thecorresponding portion of the passage can be drained.

[0214] In the stop sequence mode of the present embodiment, the valve VAis opened, the valve VB is closed or slightly opened, and the valve VCis closed. Accordingly, the flow velocity in the local generationreaction gas passage CC1 increases, so that the draining efficiency ofthe generated water is improved. Therefore, it is possible to reliablyprevent the generated water in the reaction gas passage CC1 fromfreezing. In addition, the flow velocity of the reaction gas in thereaction gas passage CC1 can be controlled by controlling the degree ofopening of the valve VB. Furthermore, the generated water generated atthe lower side of the power generation plane of the membrane electrodeassembly 5 can be drained by slightly opening the valve VB.

[0215] Since the present embodiment employs the U-shaped localgeneration reaction gas passage CC1 formed in the adjacent reaction gaspassages CC via the bypass portion 123, the passage CC1 has a crosssection smaller than that of the reaction gas passage C. The amount ofthe reaction gas supplied to the passage having such a smaller area isthe same as that of the reaction gas supplied in the entire planegeneration, so that self heating is concentratedly performed. In thelow-temperature starting mode, the flow velocity of the reaction gas isincreased and this reaction gas having an increased velocity flowsthrough a shorter passage CC1. Therefore, the local generation can befurther effectively performed.

[0216] In the present embodiment, the two oxidizing gas outletcommunication holes 212 and 213 are effectively used as the inlet andoutlet of the local generation reaction gas passage CC1 so as to supplyand discharge the reaction gas; thus, the number of structural elementscan be small. However, as shown by dashed lines in FIG. 18, two openings124 may be respectively provided in the passages CC which are adjacentvia the bypass portion 123. A branch passage is connected to the gassupply passage 16 and the end of this branch passage is connected to oneof the openings, and another branch passage is connected to the junctionpassage 19 (for the gas discharge passages 17) and the end of thisbranch passage is connected to the other of the openings, therebyforming a local generation reaction gas passage. That is, in theembodiment employing the oxidizing gas outlet communication holes 212and 213, these communication holes 212 and 213 function as theabove-explained openings 24.

[0217] Seventh Embodiment

[0218]FIG. 19 shows the general structure of a separator 67 at thecathode of this embodiment.

[0219] The separator 67 has a crank-shaped (or S-shaped) reaction gaspassage C, which consists of plural reaction gas passages CC. Theseparator 67 starts from the oxidizing gas inlet communication hole 10provided in an upper portion at the right side of the separator, andends at the oxidizing gas outlet communication hole 11 provided in alower portion at the left side of the separator.

[0220] The separator at the anode (not shown) also has a reaction gaspassage consisting of plural crank-shaped passages. That is, thisreaction gas passage at the anode starts from the fuel gas inletcommunication hole 20 provided in an upper portion at the left side ofthe separator, and ends at the fuel gas outlet communication hole 21provided in a lower portion at the right side of the separator, so as toform a crossing positions relationship with the reaction gas passage Cat the cathode. The cooling liquid system, the gas supply system, thedischarged gas processing system and the like are not shown in FIG. 19.

[0221] A communication passage 88 is provided which crosses each passageCC and makes the passages CC communicate with each other. Thiscommunication passage 88 is connected to an opening 89 (corresponding toan opening 91 at the anode) which is provided between the oxidizing gasinlet communication hole 10 and the oxidizing gas outlet communicationhole 11. The portion between the opening 89 and the oxidizing gas inletcommunication hole 10 functions as a local generation reaction gaspassage CC2.

[0222] Gas supply passages 16 are respectively connected to theoxidizing gas inlet communication hole 10 and the fuel gas inletcommunication hole 20, whereas gas discharge passages 17 arerespectively connected to the oxidizing gas outlet communication hole 11and the fuel gas outlet communication hole 21. In addition, a branchpassage 112 is connected to each gas discharge passage 17, and the(branch) end 113 of the branch passage 112 is connected to each of theopenings 89 and 91.

[0223] A valve CV is provided at each junction of the gas supply passage17, where the passages connected to each valve CV are switchable byoperating the valve CV. In FIG. 19, reference symbols P indicatepressure gages.

[0224] The function of the present embodiment will be explained below.

[0225] In the low-temperature starting mode, if the temperature of thefuel cell is equal to or below a predetermined value (e.g., 0° C.), thevalves CV are controlled to make the openings 89 and 91 communicable.Under these conditions, when the reaction gas is supplied via the gassupply passage 16 at the cathode, the reaction gas is made to flow intothe reaction gas passage C from the oxidizing gas inlet communicationhole 10, and this reaction gas is discharged via the communicationpassage 88 and the opening 89 from the gas discharge passage 17, withoutreaching the oxidizing gas outlet communication hole 11. Therefore, thereaction gas is concentratedly supplied to the local generation reactiongas passage CC2 which substantially has a shorter passage length, sothat power generation is performed in the corresponding local area ofthe membrane electrode assembly 5 and the temperature of the fuel cell 1is increased.

[0226] During the operation, when the temperature in the fuel cell 1,measured by a temperature sensor (not shown), exceeds a predeterminedvalue (e.g., 0° C.), the valve CV for switching the passage is switchedso as to close the opening 89. Accordingly, the normal power generationmode in which the reaction gas flows through the entire reaction gaspassage C is started. In the present embodiment, the pressure gages Pare used for detecting pressure loss between the gas supply passage 16and the gas discharge passage 17, so that the state of the frozengenerated water in the lower portion of the reaction gas passages CC canbe estimated.

[0227] According to the present embodiment, in addition to the effectsobtained by the above embodiments, the local generation reaction gaspassage CC2 can be formed without using the oxidizing gas outletcommunication hole 11 and the fuel gas outlet communication hole 21which are positioned in a lower area of each separator, so that thereaction gas passage CC2 is not formed in an area where water tends tobe generated. Therefore, the probability of generation of water is verylow in the reaction gas passage CC2, thereby considerably improving thereliability of the fuel cell.

[0228] Eighth Embodiment

[0229] The basic structure of this embodiment is also shown in FIG. 1.Therefore, a part of the cathode 3 and the anode 2, which corresponds tothe reaction gas passages C1 and A1, is defined as a local generationarea K1. In the present embodiment, as shown in FIG. 20 (a longitudinalsectional view of a portion of the fuel cell 1), an electric heater 33(i.e., heating device) is provided at a portion of each cooling liquidpassage R, where the portion corresponds to the local generation areaK1. The electric heater 33 comprises a thin film heater which is printedor deposited on a surface of each separator 7, on which the reaction gaspassages C1 and C2 are not formed.

[0230] In FIG. 20, reference numeral 500 indicates a cell consisting ofa separator 6, an anode 2, a solid polymer electrolyte membrane 4, acathode 3, and a separator 7. In the fuel cell 1 having plural stackedcells 500, terminals (not shown) are respectively connected to theseparator 7 at the outermost cathode and the separator 6 at theoutermost anode, so as to form a closed circuit for outputting powerfrom the fuel cell 1. In addition to the driving motor and the otherloads connected to the fuel cell, an electric heater explained below isalso driven by the output of the fuel cell 1.

[0231] As shown in FIG. 20, a temperature sensor 34 for detecting atypical temperature in the fuel cell 1 is attached to a predeterminedposition of the separator 7 of one of the cells 500. The predeterminedposition is in the local generation area K1, preferably at the center ofthe area K1. The temperature sensor 34 includes, for example, athermistor, and the output signal from the temperature sensor 34 isinput into the ECU 50.

[0232] Also in this fuel cell 1, a pressure sensor 136 is attached tothe pair of the separators 6 and 7 of each cell 500, and the outputsignal from the pressure sensor 136 is also input into the ECU 50.

[0233] The ECU 50 is also connected to the hydrogen tank H2, the motor“m” of the supercharger S/C, the valve 24 of the supply passage 23 whichis connected to the hydrogen tank H2, and the valve 14 of the supplypassage 13 which is connected to the supercharger S/C. The ECU 50 isoperated using the electric power stored in a battery (not shown).

[0234] In addition to the above-explained local generation operation inthe basic embodiment, the electric heater 33 is switched on while onlythe reaction gas passages C1 and A1 are used and no cooling liquid ismade to flow through the cooling liquid passages R.

[0235] Accordingly, current flows through the electric heater 33, andthe heat by the heating of the electric heater 33 is conducted via theseparators 6 and 7 to the anode 2, the cathode 3, and the solid polymerelectrolyte membrane 4, thereby quickly heating these portions.Therefore, the local generation in the area K1 is quickly performed,thereby promoting the self heating.

[0236] The operation of the electric heater 33 is controlled so as tosatisfy the above-explained formula (2). That is, the temperature of thelocal generation area K1 of each cell 500 can be increased to 0° C. orabove before the operation of the fuel cell 1 is stopped due to decreaseof the output voltage of the fuel cell 1, which is caused by freezing ofthe generated water. Accordingly, power generation in the localgeneration area K1 can be maintained and thus the operation of the fuelcell 1 can be maintained even if the temperature of the other area(e.g., the lower half of each cell 500) is below the freezing point. Inaddition, the minimum energy necessary for operating the fuel cell 1,which corresponds to power necessary for driving auxiliary machines suchas the supercharger S/C, can be obtained by the generation of the fuelcell 1. Furthermore, in comparison with the case of proving a heater forheating the entire plane of the cell 500, less energy is necessary,thereby suppressing power consumption in the local plane powergeneration.

[0237] A preprocess before starting the low-temperature mode includespurging in the reaction gas passages C1 and C2, preheating using theelectric heater 33, and the like. In the present embodiment, only thelocal generation area K1 must be prepared for starting thelow-temperature mode; thus, energy consumption for the preprocess can bereduced.

[0238] An example of the control for starting the fuel cell 1 will beexplained with reference to the flowchart in FIG. 21.

[0239] In the first step S101, it is determined whether the ignitionswitch is on. If the result of the determination is “YES” (i.e., theignition switch is on), the operation proceeds to step S102, while ifthe result of the determination is “NO” (i.e., the ignition switch isoff), the operation of this flow is terminated.

[0240] After step S102 in which the system is checked, it is determinedin step S103 whether the system is in the normal state. If the result ofthe determination is “YES” (i.e., no abnormal state has been found), theoperation proceeds to step S 104, while if the result of thedetermination is “NO” (i.e., the system is in an abnormal state), theoperation proceeds to step S105.

[0241] In step S104, it is determined whether a typical temperature inthe fuel cell 1, measured by the temperature sensor 34, is lower than 0°C. If the result of the determination is “NO” (i.e., the temperature isequal to or above 0° C.), the operation proceeds to step S106 so as toshift the operation mode to the entire plane generation. If the resultof the determination in step S104 is “YES” (i.e., the temperature isbelow 0° C.), the operation proceeds to step S107 so as to shift theoperation mode to the local plane generation mode.

[0242] In the local plane generation mode performed in step S107, thelocal generation using the local generation area K1 as explained aboveis performed. In the following step S108, it is determined whether thetypical temperature in the fuel cell 1 is lower than a predeterminedtemperature which is 0° C. or above. Here, this predeterminedtemperature is 2° C. If the result of the determination is “YES” (i.e.,below 2° C.), the operation returns to step S107, while if the result ofthe determination is “NO” (i.e., equal to or above 2° C.), the operationproceeds to step S106. That is, while the typical temperature in thefuel cell 1 is lower than the predetermined temperature (i.e., 2° C.),the local plane generation of the fuel cell 1 is continued, and when thetypical temperature reaches the predetermined temperature (i.e., 2° C.),the local plane generation mode is switched to the entire planegeneration mode. When the local plane generation mode is terminated, theelectric heater 33 is switched off.

[0243] In the entire plane generation mode in step S106, the entireplane power generation as explained above is performed. When theoperation proceeds to step S105, the operation mode is shifted to anabnormal state handling mode, and the operation of this flow is thenterminated.

[0244] In the above control for starting the fuel cell, the typicaltemperature in the fuel cell 1 is referred to for determining whetherthe local plane generation mode is started, and whether the mode isshifted to the entire plane generation mode. However, thesedeterminations may be performed based on the entire output voltage ofthe fuel cell 1.

[0245] Also in the above control, the electric heaters 33 of all cells500 are switched on when the local plane generation mode is started.However, the determination whether the electric heater 33 should beswitched on may be performed for each cell 500, or each group (ormodule) of plural cells 500. In this case, the cells 500 which requireheating by the electric heater 33 can be detected, thereby reducingenergy consumption in the local plane generation mode.

[0246] If the determination whether the electric heater 33 should beswitched on is performed for each cell 500, a temperature sensor 34 isprovided in each cell 500. Accordingly, the temperature of the localgeneration area K1 of each cell 500 is independently measured, and onlyfor the cell(s) whose temperature of the local generation area K1 isdetermined to be below 0° C., the electric heater 33 is switched on.When the temperature of the local generation area K1 of the relevantcell reaches 2° C., the electric heater 33 is switched off.

[0247] If the determination whether the electric heater 33 should beswitched on is performed for each cell group including plural cells, atemperature sensor 34 is provided in each cell group. Accordingly, onlyfor the group(s) whose temperature of the local generation area K1 isdetermined to be below 0° C., the electric heater 33 of each cell 500which belongs to the relevant groups is switched on. When thetemperature of the local generation area K1 of each relevant groupreaches 2° C., the corresponding electric heaters 33 are switched off.

[0248] If the temperature sensor 34 is provided for each cell 500 oreach cell group as explained above, an energy saving mode as explainedbelow may be used for controlling the ON/OFF operation of the electricheater 33 based on the remaining power of a battery (not shown).

[0249] First, when the local plane generation mode is started, it isdetermined whether the battery stores electric power sufficient formaintaining the operation of the fuel cell 1 even if all the electricheaters 33 are switched on. If the result of the determination is “YES”,the electric heaters 33 are controlled using a normal control method,while the result of the determination is “NO”, the electric heaters 33are controlled using an energy saving mode.

[0250] In the energy saving mode, typically, the rate of the voltagedecrease is calculated for each cell 500. If each cell 500 isindependently controlled, the electric heater 33 of each cell 500 whoserate of the voltage decrease is positive (i.e., the voltage hasdecreased) is switched on, and the electric heater 33 of each cell whoserate of the voltage decrease is negative (i.e., the voltage has notdecreased) is switched off.

[0251] If each cell group (consisting of plural cells) is independentlycontrolled, the electric heaters 33 of the cells of each cell group,which includes at least one cell 500 whose rate of the voltage decreaseis positive (i.e., the voltage has decreased), are switched on, and theelectric heaters 33 of the cells of each cell group, in which all thecells have a negative rate of the voltage decrease, are switched off.According to the above control, the energy consumption in the localplane generation mode can be further reduced.

[0252] In the above explanation, the area of the electric heater 33 isprovided over the area where the reaction gas passages C1 and A1 overlapwith each other. However, the electric heater 33 may be provided foronly a portion of the above overlap area, for example, a centralportion.

[0253] The position of each electric heater 33 is also not limited to bein the cooling liquid passage R, and the electric heater 33 may beembedded in each separator (6 or 7).

[0254] In the local plane generation mode, the hydrogen gas may besupplied to both the upper and lower reaction gas passages A1 and A2,and air may be supplied to both the upper and lower reaction gaspassages C1 and C2. In this case, the power generation is started fromthe local generation area K1 whose temperature is increased by theelectric heater 33, and the corresponding self heating and the heat bythe electric heater 33 are conducted over the entire generation plane,thereby starting the generation of the lower area.

[0255] Instead of the structure shown in FIG. 1, a structure shown byFIG. 22 may be employed. This structure has reaction gas passages C andA formed in a zigzag, and the reaction gas passages C and A have acrossing positional relationship (refer to FIG. 14). Here, the oxidizinggas inlet communication hole 10 and the fuel gas inlet communicationhole 20 are provided in an upper portion, while the oxidizing gas outletcommunication hole 11 and the fuel gas outlet communication hole 21 areprovided in a lower portion. In this case, the local generation area K1including an electric heater 33 may be an area where the reaction gaspassages C and A overlap with each other in an upper horizontal section(see a rectangle CA enclosed by a chain double-dashed line). Inaddition, the local generation area K1 may be defined to be smaller orwider, so as to obtain similar effects.

[0256] Ninth Embodiment

[0257] The ninth embodiment will be explained with reference to FIGS. 23and 24. The distinctive feature of this embodiment in comparison withthe previous embodiment is the position of each electric heater.

[0258] Instead of providing the electric heater 33 in a part of thecooling liquid passage R, an electric heater is built in a stud bolt forfastening the stacked cells in the present embodiment.

[0259]FIG. 23 is a plan view of the separator 7 at the cathode. In thepresent embodiment, the stacked cells are fastened using stud bolts 140(i.e., fastening bolts), which are provided at three positions in theupper side and the other three positions at the lower side. Among thesesix stud bolts 140, only one positioned at the center on the upper side,which is indicated by reference numeral 140A, includes an electricheater.

[0260]FIG. 24 is a cross-sectional view of a stud bolt 140A. Referencenumeral 51 indicates a base of the stud bolt, and an insulating layer 52is formed around the outer-peripheral surface of the base 51. Anelectric heater 53 (i.e., heating device) is provided around theinsulating layer 52, and another insulating layer 54 is further providedaround the electric heater 53. The insulating layers 52 and 54 areprovided for insulating between the electric heater 53, the base 51, andexternal portions (corresponding to the fuel cell 1 and the like), andfor providing sufficient durability to the stud bolt; therefore, theseinsulating layers have a glass-fiber base and are formed using Teflon (aregistered trademark, which is a resin) or the like. The outerinsulating layer 54 includes a temperature sensor 55. The electricheater 53 and the temperature sensor 55 are connected to a temperaturecontroller 56 for controlling the electric heater 53 in a manner suchthat the surface temperature of the stud bolt 140A, that is, the surfacetemperature of the insulating layer 54 is always within a predeterminedtemperature range (e.g., 50 to 70° C.).

[0261] In the local plane generation mode of the present embodiment, theelectric heater 53 of the stud bolt 140A is switched on so as to heatthe stud bolt 140A, so that in each cell 500, the peripheral area aroundthe stud bolt 140A is heated. Therefore, the vicinity of the stud bolt140A is defined as a local generation area K2.

[0262] In this embodiment in which the quick heating of the localgeneration area K2 generates a high-temperature portion, heat isgenerally conducted from the area K2 to the upper half of the entiregeneration plane, so that the local generation is performed and similareffects as obtained in the above embodiments can be obtained.

[0263] The number of the stud bolts 140A (which include electricheaters) may be 2 or more, and the position of the stud bolt 140A is notlimited. Also in this case, the reaction gas passages may be formed in azigzag (refer to FIG. 22).

[0264] Tenth Embodiment

[0265] The tenth embodiment will be explained with reference to FIGS. 25and 26. The distinctive feature of this embodiment in comparison withthe above eighth embodiment is a heating device for locally heating eachcell 500. In the present embodiment, instead of the electric heater 33in the eighth embodiment, a catalytic combustor is provided at aspecific position in each cell, and catalytic combustion of oxygen (inthe air) and hydrogen is performed in the catalytic combustor, so as tolocally heat the vicinity of the catalytic combustor in cell 500.

[0266]FIG. 25 is a longitudinal sectional view of a portion of the fuelcell 1, which corresponds to FIG. 20. FIG. 26 is a plan view of theseparator 6 at the anode, observed from the side where the coolingliquid passages R are formed.

[0267] Also in this embodiment, the fuel cell 1 has oxidizing gas inletcommunication holes 10, oxidizing gas outlet communication holes 11,fuel gas inlet communication holes 20, fuel gas outlet communicationholes 21, cooling liquid inlet communication holes 30, and coolingliquid outlet communication holes 31, and cooling liquid passages R andR are formed on one face of the separator 6. The other face of theseparator 6 includes reaction gas passages A1 and A2, and the separator7 has reaction gas passages C1 and C2, as explained in the eighthembodiment.

[0268] In the present embodiment, two communication holes 61 and 62 areformed between the cooling liquid outlet communication holes 31 and 31,where the communication holes 61 and 62 pass through the cell 500. Inaddition, a communication hole 63 is formed between the cooling liquidinlet communication holes 30 and 30, which also passes through the cell500. The communication hole 61 is a hydrogen gas communication hole forsupplying hydrogen, while the communication hole 62 is an aircommunication hole for supplying air. The communication hole 63 is adischarge communication hole for discharging combustion gas.

[0269] In the separator 6 of each cell 500, a gas passage 64 forcommunicating the hydrogen gas communication hole 61, the aircommunication hole 62, and the discharge communication hole 63 isprovided between the cooling liquid passages R and R and in the face onwhich the passages R and R are formed. The gas passage 64 is formed in amanner such that the passages connected to the hydrogen gascommunication hole 61 and the air communication hole 62 are joined, andthe unified passage is connected to the discharge communication hole 63.On the inner wall surface of the joining portion of these passages (seethe hatched portion in FIG. 26), a catalyst 65 (which functions as acatalytic combustor or a heating device) is adhered.

[0270] In addition, in one of the separators 7, a temperature sensor 69for detecting a typical temperature of the fuel cell 1 is provided inthe vicinity of the position (of the anode) at which the catalyst 65 isadhered. The temperature sensor 69 includes a thermistor or the like,and the signal output from the sensor is input into the ECU 50.

[0271] The hydrogen gas communication hole 61 is connected via a controlvalve 66 to a hydrogen supply system 167, and the air communication hole62 is connected to an air supply system 168. The control valve 66, thehydrogen supply system 167, and the air supply system 168 are controlledby the ECU 50.

[0272] In comparison with the low-temperature starting mode of the aboveeighth embodiment, which uses the electric heater 33, in thelow-temperature starting mode of the present embodiment, the hydrogengas is supplied from the hydrogen supply system 167 to the hydrogencommunication hole 61, while the air is supplied from the air supplysystem 168 to the air communication hole 62, so that the hydrogen gasdrawn from the communication hole 61 into the gas passage 64 and the airdrawn from the communication hole 62 into the gas passage 64 react bythe catalyst 65 at the conjunction of the gas passage. According to theheat generated by the reaction, the vicinity of the conjunction isconcentratedly heated. Therefore, a local generation area K3 can also beformed in the present embodiment, and similar function and effects canbe obtained.

[0273] In addition, in the present embodiment of employing the catalyticcombustion, a large quantity of thermal energy can be obtained, and thetemperature increases very sharply. Therefore, in comparison with usingthe electric heater 33, quicker heating can be performed. Furthermore,hydrogen also functions as the fuel of the fuel cell 1; thus, acentralized fuel supply system can be established, thereby simplifyingthe system structure.

[0274] An example of the control for starting the fuel cell 1 will beexplained with reference to the flowchart in FIG. 27.

[0275] Steps S201 to S205 in FIG. 27 are the same as steps S101 to S105in the eighth embodiment; thus, explanations thereof are omitted.

[0276] In the present embodiment, if the result of the determination instep S204 is “NO” and the entire plane generation mode is started instep S206, the supply of hydrogen for combustion from the hydrogensupply system 167 to the hydrogen gas communication hole 61 is stoppedand the supply of air from the air supply system 168 to the aircommunication hole 62 is also stopped. Simultaneously, cooling liquid ismade to flow through the cooling liquid passages R and R, the hydrogengas is supplied to the reaction gas passages A1 and A2, and the air issupplied to the reaction gas passages C1 and C2, so that powergeneration using the entire generation plane of each cell 500 isperformed.

[0277] If the result of the determination in step S204 is “YES” and thelocal plane generation mode is started in step S207, no cooling liquidis made to flow through the cooling liquid passages R and R, andhydrogen and air are respectively supplied to only the reaction gaspassages A1 and C1 formed in the upper half of each cell 500.Simultaneously, air for combustion is supplied from the air supplysystem 168 to the air communication hole 62 and hydrogen for combustionis supplied from the hydrogen supply system 167 to the hydrogencommunication hole 61, thereby performing the local generation in thelocal generation area K3. In accordance with the typical temperature inthe fuel cell 1, the amount of hydrogen supplied for combustion isdetermined by the ECU 50 which refers to a data map which is defined andstored in a memory in advance. Based on the determined amount ofhydrogen supply, the ECU 50 performs flow control using the controlvalve 66.

[0278] In step S208, it is determined whether the typical temperature inthe fuel cell 1 is lower than a predetermined temperature which is 0° C.or above. Here, this predetermined temperature is 2° C. If the result ofthe determination is “YES” (i.e., below 2° C.), the operation returns tostep S207 and the local plane generation is continued, while if theresult of the determination is “NO” (i.e., equal to or above 2° C.), theoperation proceeds to step S206 and the entire plane generation isperformed.

[0279] In the above control for starting the fuel cell 1, the typicaltemperature in the fuel cell 1 is referred to for determining whetherthe local plane generation mode is started, and whether the mode isshifted to the entire plane generation mode. However, thesedeterminations may be performed based on the entire output voltage ofthe fuel cell 1. This variation may also be applied to a similarembodiment which employs a local plane generation mode.

[0280] Also in the above control, the entire plane generation mode isstarted if the typical temperature of the fuel cell 1 is higher than 0°C. However, even when the typical temperature of the fuel cell 1 isabove 0° C., if the temperature is relatively low (e.g., 15° C. orbelow), gentle warming up of the fuel cell 1 may be performed bysupplying a small amount of hydrogen and air for combustion to the gaspassage 64, so as to increase the temperature of the fuel cell 1. Suchgentle warming up may be performed when at least one cell 500 hasvoltage decrease, in addition to the above condition for executing thegentle warming up.

[0281] Similar to the eighth embodiment, hydrogen and air may besupplied to the entire reaction gas passages (A1, A2, C1, and C2) in thelocal plane generation mode, and the shape of each reaction gas passagemay be freely modified.

[0282] Eleventh Embodiment

[0283] The eleventh embodiment will be explained with reference to FIGS.28 and 29. The structure of this embodiment is very similar to that ofthe previous embodiment. The distinctive feature of the presentinvention in comparison with the previous (i.e., tenth) embodiment isthat an oxidizing and reducing agent is provided at a specific area ofeach cell 500, so as to locally heat the cell 500 by using heatgenerated when the oxidizing and reducing agent is oxidized by oxygen.

[0284]FIG. 28 is a longitudinal sectional view corresponding to FIG. 25in the tenth embodiment, which shows a portion of the fuel cell 1 of thepresent embodiment. FIG. 29 also corresponds to FIG. 26 in the tenthembodiment.

[0285] In the present embodiment, a communication hole 170 passingthrough the cell 500 is formed between the cooling liquid outletcommunication holes 31 and 31. This gas communication hole 170 isconnected to the hydrogen supply system 167 and the air supply system168. In the separator 6, a gas passage 71 for connecting the gascommunication hole 170 and the discharge communication hole 63 isprovided between the cooling liquid passages R and R. On the inner wallsurface of a portion of the upstream of the gas passage 71, that is, inthe vicinity of the gas communication hole 170, an the oxidizing andreducing agent 72 (i.e., heating device) is adhered (see the hatchedportion in FIG. 29).

[0286] In the local generation mode of the previous embodiment, hydrogenand air are simultaneously supplied to the gas passage 64 so as to makethem react by the catalyst at the junction of the passage. However, inthe local generation mode of this embodiment, only air is supplied tothe gas communication hole 170 from the air supply system 168, that is,hydrogen is not supplied to the communication hole 170. Accordingly, theair supplied to the gas communication hole 170 is drawn into the gaspassage 71 of each cell 500, and the oxidizing and reducing agent 72 atthe upstream of the passage 71 reacts with oxygen in the supplied air,so that heat, which is generated by the reaction, locally heats thevicinity of the area where the oxidizing and reducing agent 72 isadhered in the upstream of the gas passage 71. Therefore, also in theeleventh embodiment, a local generation area K4 can be provided andsimilar effects to those obtained by the tenth embodiment can beobtained.

[0287] In the eleventh embodiment, when the local plane generation modeis terminated, the air supply to the gas communication hole 170 isstopped, and a specific amount of hydrogen is supplied from the hydrogensupply system 167 to the gas communication hole 170. Accordingly, theoxidizing and reducing agent 72 reacts with hydrogen and returns to theoriginal agent. In this process, the oxidizing and reducing agent 72receives heat.

[0288] Twelfth Embodiment

[0289] The twelfth embodiment will be explained with reference to FIGS.30 and 31.

[0290] In the above embodiments, the local generation area is defined atthe same position in each cell 500. However, in this embodiment, thelocal generation area K is defined at a different position between theadjacent cells 500. In FIG. 30, reference numeral 500-1 indicates an Xthcell 500, and reference numeral 500-2 indicates an (X+1)th cell 500.Accordingly, when current flows between these cells 500 in the localplane generation mode, the current flows between the separators 6 and 7in a direction perpendicular to the stacking direction of the cells 500(i.e., the direction in which the cells are stacked), as shown by arrowQ in FIG. 31. Therefore, Joule heat corresponding to a (thermal) lossproduced by the electric resistance of the separators 6 and 7 isgenerated, thereby further promoting the warming up of the fuel cell 1.

[0291] The method of providing the local generation area K is notlimited; however, using an electric heater as is used in the eighthembodiment is most preferable, and a catalytic combustor or an oxidizingand reducing agent may be used, as is used in the tenth and eleventhembodiments.

[0292] All the adjacent cells may define a different position for thelocal generation area K, or the position may be different for each groupor module of cells.

[0293] Thirteenth Embodiment

[0294] The structure of the thirteenth embodiment will be explained withreference to FIGS. 32 to 34.

[0295]FIG. 32 is a plan view of the separator 6 at the anode, observedfrom the side where the cooling liquid passages R and R are formed. FIG.33 is a longitudinal sectional view of a portion of the fuel cell 1.FIG. 34 is a plan view of the separator 6, observed from the side wherethe reaction gas passages A1 and A2 are formed. A cooling liquid circuitand a control system are also shown in FIG. 32, and the reaction gaspassages C1 and C2 corresponding to the reaction gas passages A1 and A2are also shown by dashed lines in FIG. 34.

[0296] In the fuel cell 1, the oxidizing gas inlet communication holes10, the oxidizing gas outlet communication holes 11, the fuel gas inletcommunication holes 20, the fuel gas inlet communication holes 21, thecooling liquid inlet communication holes 30, and the cooling liquidoutlet communication holes 31 pass through the cells 500 in the stackingdirection of the cells.

[0297] In this embodiment, in addition to the cooling liquid passages Rand R, a second cooling liquid passage 36 is formed on the same face ofthe anode of each cell 500. The cooling liquid may be pure water,ethylene glycol, oil or the like. As shown in FIG. 33, cooling liquidpasses along both the back faces of the separators 6 and 7.

[0298] A cooling liquid inlet communication hole 38 and a cooling liquidoutlet communication hole 39, provided at either side of the secondcooling liquid passage 36, also pass through the cells 500. Therefore,three cooling liquid passages (i.e., right, center, and left) are formedin this fuel cell 11, and cooling liquid supplied to each of the inletcommunication holes 30, 38, and 30 are drained from each of the outletcommunication holes 31, 37, and 31.

[0299] The second cooling liquid passage 36 between the cooling liquidpassages R and R has a labyrinth passage 36 a having a spiral form inthe vicinity of the cooling liquid outlet communication hole 37. Thislabyrinth passage 36 a is provided for increasing the passage length ofthis area and increasing the residence time of the cooling liquid. Theposition of the labyrinth passage 36 a is in the upper half of theseparator 6, that is, in an area corresponding to the upper reaction gaspassages A1 and C1.

[0300] The cooling liquid passages R and R, and the second coolingliquid passage 36 cover almost the entirety of the area where thereaction gas passages A1 and C1 overlap with each other and the reactiongas passages A2 and C2 overlap with each other. This overlap areafunctions as the generation plane.

[0301] In the present embodiment, a temperature sensor 34 is provided ineach unit module which includes a specific number of cells. As shown inFIG. 33, the temperature sensor 34 is provided in the separator 7 of onecell in the unit module. As shown in FIG. 32, the temperature sensor 34is positioned in the vicinity of the labyrinth passage 36 a, so as tomeasure the temperature of the vicinity of the labyrinth passage 36 a.The signal output from the temperature sensor 34 is input into an ECU 35for controlling the fuel cell 1. The ECU 35 is operated by electricpower stored in a battery (not shown).

[0302] The cooling liquid inlet communication holes 30 and 30 areconnected via a first cooling liquid (circulating) circuit 751 to thecooling liquid outlet communication holes 31 and 31. The first coolingliquid circuit 751 has a pump 752, control valves V1 and V2 attached atthe upstream and downstream of the pump 752, and a radiator 757 providedbetween the control valve V2 and the cooling liquid outlet communicationholes 31 and 31.

[0303] The control valves V1 and V2 function as switching devices forcontrolling the passages for cooling liquid. When the control valves V1and V2 are opened, the circulation of the cooling liquid through thecommunication holes 30 and 31 is permitted, so that the cooling liquidpasses through the cooling liquid passages R and R. When the controlvalves V1 and V2 are closed, the circulation of the cooling liquidthrough the communication holes 30 and 31 is prohibited, so that thecooling liquid does not pass through the cooling liquid passages R andR.

[0304] A cooling liquid passage 753 is connected between the pump 752and the control valve V1, and the cooling liquid passage 753 isconnected to the cooling liquid outlet communication hole 37. Inaddition, a cooling liquid passage 754 is connected between the pump 752and the control valve V2, and the cooling liquid passage 754 isconnected to the cooling liquid inlet communication hole 38.Accordingly, the second cooling liquid passage 36 is connected via thecommunication holes 37 and 38 and the cooling liquid passages 753 and754 to the first cooling liquid circuit 751 in parallel to the coolingliquid passages R and R.

[0305] The cooling liquid can always pass through the cooling liquidpassages 753 and 754 regardless of the opening/closing states of thecontrol valves V1 and V2; thus, while the pump 752 is driven, thecooling liquid flows through the second cooling liquid passage 36 viathe communication holes 38 and 37. In the present embodiment, thecooling liquid passages 753 and 754 are constituents of a second coolingliquid (circulating) circuit.

[0306] An electric heater 755 (i.e., heating device) is provided at aportion of the cooling liquid passage 754, so that the cooling liquidpassing through the cooling liquid passage 754 can be heated byswitching on the electric heater 755. This electric heater 755 iscontrolled by the ECU 35 so that the temperature of the cooling liquidwhich flows through the cooling liquid passage 754 can be controlled.

[0307] In addition, a temperature sensor 756 for detecting thetemperature of the cooling liquid which flows through the cooling liquidpassage 754 is attached to the cooling liquid passage 754, where theposition of the temperature sensor 756 is between the electric heater755 and the cooling liquid inlet communication hole 38. The signaloutput from the temperature sensor 756 is input into the ECU 35.

[0308] In the entire plane generation mode of the present embodiment,while the entire plane generation as explained above is performed, thecooling liquid is made to flow through all the cooling liquid passages Rand R, and the second cooling liquid passage 36. That is, the pump 752is driven and the control valves V1 and V2 are opened so as to supplycooling liquid to the cooling liquid inlet communication holes 30, 38,and 30. The flows of the cooling liquid pass through the cooling liquidpassages R, 36, and R and are then discharged from the correspondingoutlet communication holes 31, 37, and 31. Accordingly, the entiregeneration plane of each cell is cooled by the cooling liquid during theentire plane generation.

[0309] In this entire plane generation mode, the radiator 757 providedin the first cooling liquid circuit 751 is driven so as to cool thecooling liquid, and the electric heater 755 is switched off so as not toheat the cooling liquid flowing through the cooling liquid passage 754.

[0310] On the other hand, in the local plane generation mode of thepresent embodiment, while the local plane generation as explained aboveis performed by using only the upper half of the entire plane, the pump752 is driven and the control valves V1 and V2 are closed, so that thecooling liquid cannot pass through the cooling liquid inlet and outletcommunication holes 30 and 31. Therefore, no cooling liquid flowsthrough the cooling liquid passages R and R, and the cooling liquid inthe first cooling liquid circuit 751 circulates in a closed circuit of“pump 752→first cooling liquid circuit 751→cooling liquid passage754→cooling liquid inlet communication hole 38→second cooling liquidpassage 36→cooling liquid outlet communication hole 37→cooling liquidpassage 753→first cooling liquid circuit 751→pump 752”. Therefore, inthis process, no cooling liquid passes through the radiator 757; thus,the cooling liquid is not cooled. Also in this local plane generationmode, the electric heater 755 is switched on, so as to heat the coolingliquid passing through the cooling liquid passage 754.

[0311] Accordingly, the cooling liquid heated by the electric heater 755flows upward only through the second cooling liquid passage 36, so thatthe vicinity of the labyrinth passage 36 a, where the residence time ofthe cooling liquid is long, is concentratedly heated. The heat isconducted via the separators 6 and 7 to the relevant areas of the anode2, the cathode 3, and the solid polymer electrolyte membrane 4, andthese areas are quickly heated. Therefore, also in the presentembodiment, a local generation area K is formed in the vicinity of thelabyrinth passage 36 a.

[0312] The quantity of heating using the electric heater 755 for heatingthe cooling liquid is controlled so as to satisfy the above-explainedformula (2), thereby avoiding freezing of water generated in the fuelcell during power generation. Therefore, the temperature of the localgeneration area K of each cell 500 can be 0° C. or more before the fuelcell 1 is stopped due to voltage decrease caused by the frozen generatedwater, that is, before the output voltage of the fuel cell 1 decreasesto the limit voltage at which the fuel cell can operate. Accordingly,the power generation in the local generation are K can be maintained;thus, the generation of the fuel cell 1 can be continued even if thetemperature of the other portion (e.g., the lower half of each cell 500)is below the freezing point.

[0313] The heat generated by the self heating of the local generationarea K and the heat of the heated cooling liquid in the labyrinthpassage 36 a gradually expand, so that the area where the powergeneration can be performed increases and the fuel cell 1 can be quicklywarmed up, as explained in the above embodiments.

[0314] Additionally, in comparison with the case in which heated coolingliquid is made to flow through the cooling liquid passages R and R so asto heat the entire plane of each cell 500, the local plane generationmode which targets the local generation area K requires less energy,thereby suppressing power consumption in the local plane generationmode.

[0315] When a preprocess (such as preheating) performed before startingthe operation of the fuel cell is executed, only the local generationarea K must be prepared; thus, energy consumption for the preprocess canbe reduced.

[0316] Also in this embodiment, only one pump 752 is necessary; thus,the increase of the number of necessary parts and the cost can besuppressed.

[0317] An example of the control for starting the fuel cell 1 in thisembodiment will be explained with reference to the flowchart in FIG. 35.

[0318] Steps S301 to S303, and S305 in FIG. 35 are the same as stepsS101 to S103, and S105 in the eighth embodiment; thus, explanationsthereof are omitted.

[0319] In step S304, a temperature Tjt detected by one of thetemperature sensors 34 provided for each unit module (of the cells) isreferred to as a typical temperature in the local generation area K ofthe fuel cell 1, and it is determined whether this temperature Tjt isbelow 0° C. If the result of the determination is “NO” (i.e., 0° C. orabove), the operation proceeds to step S304 and the entire planegeneration mode is started.

[0320] If the result of the determination in step S304 is “YES” (i.e.,below 0° C.), the local plane generation mode is started in step S307and the above-explained local plane generation is performed, in which(i) hydrogen and air are supplied to only the upper reaction gaspassages A1 and C1, (ii) the control valves V1 and V2 are closed so asto make the cooling liquid not to flow through the cooling liquidpassages R and R but to flow only through the second cooling liquidpassage 36, and (iii) the electric heater 755 is switched on so as tocirculate the heated cooling liquid through the second cooling liquidpassage 36. The output of the electric heater 755 is controlled by ECU35 so as to set the temperature of the cooling liquid supplied to thesecond cooling liquid passage 36 to a predetermined temperature (e.g.,70° C.) or below.

[0321] In the following step S308, temperature T0 of the cooling liquid,measured by the temperature sensor 756, and temperature Tj of the localgeneration area K in each unit module (of the cells), measured by thetemperature sensor 34, are stored in a memory of ECU 35, and theoperation proceeds to step S309.

[0322] In step S309, it is determined whether the temperature Tj of thelocal generation area K of each unit module is lower than thetemperature T0 of the cooling liquid. If the result of the determinationis “YES” (i.e., Tj<T0), the operation returns to step S307, while if theresult of the determination is “NO” (i.e., Tj≧T0), the operationproceeds to step S306. That is, the local power generation for warmingup the fuel cell 1 is continued until the temperature Tj of the localgeneration area K of each unit module reaches the temperature T0 of thecooling liquid which passes through the second cooling liquid passage36. When the temperature Tj of the local generation area K of each unitmodule reaches the temperature T0, the local plane generation mode isterminated and the mode is shifted to the entire plane generation mode.When the local plane generation mode is terminated, the electric heater755 is switched off and the control valves V1 and V2 are opened.

[0323] In the entire plane generation mode in step S306, theabove-explained entire plane generation is performed, that is, (i) thecontrol valves V1 and V2 are opened so as to make the cooling liquidpass through the three cooling liquid passages R, 36, and R, (ii)hydrogen and air is supplied all the reaction gas passages A1, A2, C1,and C2, and (iii) the electric heater 755 is switched off.

[0324] Instead of comparing the temperature Tj of the local generationarea K of each module with the temperature T0 of the cooling liquid, thetypical temperature in the fuel cell 1 may be compared with a specifictemperature so as to determine whether the local plane generation modeis continued or whether the mode is shifted to the entire planegeneration mode.

[0325] In addition, the temperature sensor 34 may be provided for eachcell 500, and the selection between the continuation of the local planegeneration mode and the mode shift to the entire plane generation modemay be performed by determining whether the temperature of the localgeneration area K of each cell 500 is below a predetermined temperature(e.g., temperature T0 of the cooling liquid or another specifictemperature).

[0326] In the above explanation, the second cooling liquid passage 36 isarranged at the center in the width direction of the cell 500. However,the position of the second cooling liquid passage 36 is not limited,that is, the position can be suitably defined based on the form of eachreaction gas passage (for hydrogen or air in this embodiment) or thelike.

[0327] In the local plane generation mode of this embodiment, eachreaction gas may be supplied to the upper and lower reaction gaspassages. Also in this case, power generation starts in the localgeneration are K by the heated cooling liquid, and the heat, generatedby the self heating and the heated cooling liquid, gradually expands sothat the entire plane generation starts according to the increase of thetemperature of the entire generation plane.

[0328] In addition, reaction gas passages A and C formed in a zigzag(refer to FIG. 22 in the eighth embodiment) may be employed also in thiscase (see FIG. 36). In this structure, each of the hydrogen gas and theair flows downward in a zigzag. Preferably, a labyrinth passage 36 a isformed at the center in an area where the reaction gas passages A and Coverlap in an upper horizontal section. Accordingly, a local generationarea K enclosed by a chain double-dashed line in FIG. 36 can be defined.Also in this case, another arrangement of the local generation area K ispossible by providing the labyrinth passage 36 a at a differentposition. In either arrangement of the present embodiment, functions andeffects which are similar to those of the above embodiments can beobtained.

[0329] Fourteenth Embodiment

[0330] The structure of the fourteenth embodiment will be explained withreference to FIGS. 37 and 38. The basic structure of the fuel cell 1 ofthis embodiment is the same as that of the previous (i.e., thirteenth)embodiment. The distinctive feature of the present embodiment incomparison with the previous embodiment is to have a cooling liquidcircuit which is used in the local plane generation and is independentof the first cooling liquid circuit. Below, this distinctive featurewill be explained in detail.

[0331]FIG. 37 is a plan view of the separator 6 at the anode, observedfrom the side where the cooling liquid passages R and R and the secondcooling liquid passage 36 are formed. FIG. 37 also shows a coolingliquid circuit and a control system; thus, FIG. 37 corresponds to FIG.32.

[0332] In the present embodiment, the cooling liquid inlet communicationholes 30 and 30 are connected via a first cooling liquid (circulating)circuit 861 to the cooling liquid outlet communication holes 31 and 31.The first cooling liquid circuit 861 has a pump 863 (i.e., “P1” in FIG.37) and a radiator 867. On the other hand, the cooling liquid inletcommunication hole 38 is connected via a third cooling liquid circuit862 to the cooling liquid outlet communication hole 37, and the thirdcooling liquid circuit 862 has a pump 864 (i.e., “P2” in FIG. 37). Thefirst and third cooling liquid circuits 861 and 862 are independent ofeach other, and no cooling liquid communicates between the first andthird cooling liquid circuits 861 and 862.

[0333] An electric heater 865 (i.e., heating device) for heating thecooling liquid flowing through the third cooling liquid circuit 862 isprovided in the middle of the third cooling liquid circuit 862. Inaddition, a temperature sensor 866 for detecting the temperature of thecooling liquid flowing through the third cooling liquid circuit 862 isattached to the third cooling liquid circuit 862. The electric heater865 and the temperature sensor 866 correspond to the electric heater 755and the temperature sensor 756. In the present embodiment, the first andthird cooling liquid circuits 861 and 862 are independent of each other,and each circuit has a pump (863 or 864). Therefore, the control valvesV1 and V2 provided in the previous embodiment are not used in thisembodiment. The other structural elements are the same as those in theprevious embodiment.

[0334] In the entire plane generation mode of this embodiment, theelectric heater 865 is switched off and the pumps 863 and 864 are drivenso as to circulate the cooling liquid through the first and thirdcooling liquid circuits 861 and 862, so that the cooling liquid flowsthrough the cooling liquid passages R and R, and the second coolingliquid passage 36, thereby cooling the entire generation plane.

[0335] In local plane generation mode of this embodiment, the electricheater 865 is switched on and only the pump 864 (among two pumps) isdriven so as to circulate the cooling liquid through the third coolingliquid circuit 862. The other pump 863 is stopped so as not to circulatethe cooling liquid through the first cooling liquid circuit 861.Accordingly, in the local plane generation mode, no cooling liquid flowsthrough the cooling liquid passages R and R, and the cooling liquidheated by the electric heater 865 flows only through the second coolingliquid passage 36. Therefore, similar to the first embodiment, thevicinity of the labyrinth passage 36 a can be concentratedly heated,thereby forming a local generation area K.

[0336] Therefore, functions and effects which are similar to those ofthe previous embodiment can also be obtained in the present embodiment.Additionally, according to the present structure having independent(i.e., first and third) cooling liquid circuits 861 and 862, the amountof the cooling liquid maintained in the local plane generation mode isless than that in the previous embodiment; thus, the cooling liquidsupplied to the second cooling liquid passage 36 can be rapidly heated,thereby quickly executing the local power generation.

[0337] An example of the control for starting the fuel cell 1 in thisembodiment will be explained with reference to the flowchart in FIG. 38.

[0338] Steps S401 to S405 in FIG. 38 are the same as steps S301 to S305in the previous embodiment (see FIG. 35); thus, explanations thereof areomitted.

[0339] In the present embodiment, if the result of the determination instep S404 is “NO” and the entire plane generation mode is started instep S406, both pumps 863 and 864 are driven so that the cooling liquidis made to flow through the cooling liquid passages R and R, and thesecond cooling liquid passage 36. Simultaneously, the reaction gases aresupplied to all the reaction gas passages (i.e., A1, A2, C1, and C2),thereby performing the entire plane generation using the entiregeneration plane of the fuel cell 1. In this process, the cooling liquidflowing through the first cooling liquid circuit 861 is cooled by theradiator 867. In addition, the electric heater 865 is switched off, sothat the cooling liquid flowing through the third cooling liquid circuit862 is not heated.

[0340] If the result of the determination in step S404 is “YES” and thelocal plane generation mode is started in step S407, hydrogen and airare supplied only to the reaction gas passages positioned in the upperhalf of the generation plane (i.e., A1 and C1), and the pump 863 isstopped so as not to make the cooling liquid flow through the coolingliquid passages R and R. Simultaneously, the pump 864 is driven so as tomake the cooling liquid flow only through the second cooling liquidpassage 36, and the electric heater 865 is switched on so as to heat thecooling liquid and to circulate the heated cooling liquid through thesecond cooling liquid passage 36. Accordingly, the local powergeneration in the local generation area K is performed. In this process,the output of the electric heater 865 is controlled by the ECU 35, sothat the cooling liquid has a specific temperature (e.g., 70° C.) orbelow.

[0341] In step S408, temperature T0 of the cooling liquid, measured bythe temperature sensor 866, and temperature Tj of the local generationarea K in each unit module, measured by the temperature sensor 34, arestored in ECU 35, and the operation proceeds to step S409.

[0342] In step S409, it is determined whether the temperature Tj of thelocal generation area K of each unit module is lower than thetemperature T0 of the cooling liquid. If the result of the determinationis “YES” (i.e., Tj<T0), the operation returns to step S407, while if theresult of the determination is “NO” (i.e., Tj≧T0), the operationproceeds to step S406, so that the operation mode is shifted to theentire plane generation mode. According to this mode shift, the electricheater 865 is switched off and the pumps 863 and 864 are driven.

[0343] Also in this embodiment, the form of each reaction gas passage isnot limited, for example, the reaction gas passages may be formed in azigzag (refer to FIG. 36).

What is claimed is:
 1. A fuel cell comprising: a membrane electrodeassembly in which an anode and a cathode are provided on either side ofa solid polymer electrolyte membrane; wherein: the membrane electrodeassembly has a generation plane for outputting power and at least a partof the generation plane is defined as a local generation area to which areaction gas is supplied so as to locally generate power.
 2. A fuel cellas claimed in claim 1, wherein: one of an entire plane generation mode,in which the entire generation plane is used for generation, and a localplane generation mode, in which the local generation area is used forlocally generating power, is switchably selected based on a temperatureof the generation plane.
 3. A fuel cell comprising: a membrane electrodeassembly in which an anode and a cathode are provided on either side ofa solid polymer electrolyte membrane; and a pair of separators betweenwhich the membrane electrode assembly is placed, wherein the membraneelectrode assembly is supported by the separators, wherein: a reactiongas passage is formed between the membrane electrode assembly and eachseparator, wherein a starting-mode reaction gas passage system forsupplying a reaction gas to a part of the reaction gas passage so as tolocally generate power, and a normal-mode reaction gas passage systemfor supplying a reaction gas to the entire reaction gas passage so as tonormally generate power are defined, and one of the starting-modereaction gas passage system and the normal-mode reaction gas passagesystem is switchably selected.
 4. A fuel cell as claimed in claim 3,wherein: one of the starting-mode reaction gas passage system and thenormal-mode reaction gas passage system is switchably selected based ona temperature of the generation plane.
 5. A fuel cell comprising: a cellin which an anode and a cathode are provided on either side of a solidpolymer electrolyte membrane, and a reaction gas passage is formed ateach outer side of the pair of the anode and the cathode, wherein: thecell has a generation plane for outputting power, and a heating devicefor locally heating the generation plane is provided at a part of thegeneration plane.
 6. A fuel cell as claimed in claim 5, wherein theheating device is an electric heater.
 7. A fuel cell as claimed in claim6, comprising: a plurality of the cells which are stacked; and a studbolt for fastening the stacked cells, wherein the electric heater isbuilt in the stud bolt.
 8. A fuel cell as claimed in claim 5, whereinthe heating device is a catalytic combustor.
 9. A fuel cell as claimedin claim 5, wherein the heating device includes an oxidizing andreducing agent which generates heat when being oxidized.
 10. A fuel cellsystem comprising: a fuel cell as claimed in claim 5; and a controllerfor controlling the heating device according to a temperature in thefuel cell.
 11. A fuel cell system comprising: a fuel cell as claimed inclaim 5; and a controller for controlling the heating device accordingto an output voltage of the fuel cell.
 12. A fuel cell systemcomprising: a fuel cell as claimed in claim 5, including a plurality ofthe cells which are stacked; and a controller for controlling theheating device according to a temperature of each cell.
 13. A fuel cellsystem comprising: a fuel cell as claimed in claim 5, including aplurality of the cells which are stacked; and a controller forcontrolling the heating device according to an output voltage of eachcell.
 14. A fuel cell as claimed in claim 5, comprising: a plurality ofthe cells which are stacked, wherein: in at least one pair of theadjacent cells, the heating device is provided at a different positionin the generation plane.
 15. A fuel cell system comprising: a fuel cellas claimed in claim 5; and a controller for controlling the heatingdevice to generate a quantity of heat by which refreezing of generatedwater in the fuel cell is avoided.
 16. A fuel cell comprising: a cell inwhich an anode and a cathode are provided on either side of a solidpolymer electrolyte membrane, and a reaction gas passage is formed ateach outer side of the pair of the anode and the cathode, and a firstcooling liquid passage, separated from the reaction gas passage, isformed at a further outer side, wherein: the cell has a generation planefor outputting power; a second cooling liquid passage, independent ofthe first cooling liquid passage, is formed on a part of the generationplane; and cooling liquid, heated by an external heating device which isprovided outside the cell, is suppliable to the second cooling liquidpassage.
 17. A fuel cell system comprising: a fuel cell as claimed inclaim 16; and a controller for determining whether the heated coolingliquid is supplied to the second cooling liquid passage.
 18. A fuel cellsystem as claimed in claim 17, further comprising: a first coolingliquid circuit to which the first cooling liquid passage is connected; asecond cooling liquid circuit which has said heating device for heatingthe cooling liquid, wherein the second cooling liquid passage isconnected via the second cooling liquid circuit to the first coolingliquid circuit in parallel to the first cooling liquid passage; and apassage switching section for permitting or prohibiting communication ofthe cooling liquid through the first cooling liquid passage.
 19. A fuelcell system as claimed in claim 18, wherein the passage switchingsection is controlled according to a temperature in the fuel cell.
 20. Afuel cell system as claimed in claim 17, further comprising: a firstcooling liquid circuit to which the first cooling liquid passage isconnected; a third cooling liquid circuit to which the second coolingliquid passage is connected, wherein the third cooling liquid circuithas said heating device for heating the cooling liquid and isindependent of the first cooling liquid circuit.
 21. A fuel cell systemcomprising: a fuel cell as claimed in claim 16; and a controller forcontrolling the heating device to generate a quantity of heat by whichrefreezing of generated water in the fuel cell is avoided.
 22. A fuelcell comprising: a membrane electrode assembly in which an anode and acathode are provided on either side of a solid polymer electrolytemembrane, wherein: the membrane electrode assembly has a generationplane for outputting power and at least a part of the generation planeis defined as a local generation area to which a reaction gas issupplied so as to locally generate power; and the local generation areais defined as a starting-mode power output area, and power is outputfrom only the starting-mode power output area in the local planegeneration mode.